Rafael Nadal posed with crutches and an apparently bandaged foot as the injured former US Open champion revealed on Saturday he has undergone treatment in Barcelona.

The 20-time grand slam winner announced in August that his season was over, as he battles a problem that has troubled him since 2005 and has recently hindered his tournament preparation.

Nadal felt he was unable to do himself justice, and since a French Open semi-final defeat to Novak Djokovic in June, he has played just two more matches, reaching the last 16 at the Citi Open in Washington.

He wrote on Instagram on Saturday: "Hello everyone, I have not communicated with you through the networks for some time.

"I can tell you that I was in Barcelona with my team and the medical team, to receive a treatment on my foot that will mean I take a few days of rest and a few weeks off court.

"I am back home and in the process of recovery. Thank you all for your support!"

The social media post shows Mallorca native Nadal giving a thumbs-up gesture to the camera, but it also gives an indication of the extent of his problem.

He stands with only his right foot on the ground, the left raised off the floor in what looks like an effort to protect it, as he props himself up with a pair of crutches in his left hand.

Nadal has won the US Open four times, most recently in 2019, but has been one of a number of star-name absentees from this year's tournament in New York.

The 35-year-old has 13 French Open wins among his haul of majors, and stands level on 20 grand slams with Roger Federer and Novak Djokovic.

Djokovic has an opportunity to go top of the all-time men's list on Sunday when he faces Daniil Medvedev in the men's final at Flushing Meadows.

As Nadal suffers, so does his great rival Federer. A Nadal return to action in 2022 appears a more likely prospect than another Federer comeback.

Federer has cast some doubt on whether he will play again, as the 40-year-old battles knee trouble. The Swiss said last month he would be "on crutches for many weeks" after surgery, declaring he wanted to give himself "a glimmer of hope" of featuring again on tour.

Carlos Alcaraz was lost for words after making history in the Spanish teenager's shock five-set upset of world number three Stefanos Tsitsipas at the US Open.

Alcaraz – rated by many as Spain's best young male player since 20-time grand slam champion Rafael Nadal first emerged – sent Tsitsipas packing 6-3 4-6 7-6 (7-2) 0-6 7-6 (7-5) in the third round on Friday.

The 18-year-old Alcaraz became the youngest player to reach the last 16 of the US Open since Americans Michael Chang and Pete Sampras in 1989.

Alcaraz also became the youngest man to beat a top-three opponent at the tournament since the ATP introduced its world ranking system in 1973.

After more than four hours on Arthur Ashe Stadium, Alcaraz told reporters: "I have not words to explain how I feeling right now.

"I just don't know what happened out there in the court. I can't believe that I beat Stefanos Tsitsipas in an epic match.

"For me it's a dream come true."

Amid comparisons with countryman Nadal, Alcaraz added: "Honestly I don't copy any style of a players. I just play my game.

"But if I have to say one player that is similar my game, I think it's [Roger] Federer. I think similar as mine game, trying to be aggressive all the time. I think it's a good similar for me."

After his US Open campaign came to a surprise end, third seed Tsitsipas tipped Alcaraz for future success.

"A hundred percent," Tsitsipas replied when asked if he had a sense of Alcaraz's potential. "I said he can be a contender for Grand Slam titles. He has the game to be there."

"I've never seen someone hit the ball so hard," French Open runner-up Tsitsipas added. "Took time to adjust. Took time to kind of develop my game around his game style.

"It's one of these matches and one of these feelings where, you know, you pick up at some point of the match, you feel like you're in control, and it doesn't really go your way at the end.

"It's kind of bitter, I would say, especially after such an incredible first set by my side, dominating, being just so aggressive, not dwelling on the past. It was a great first set.

"I don't know. I felt like he played the fifth one completely -- the way he played the first set basically, careless, going for every single shot. I have never seen someone play such a good fifth set, honestly."

Novak Djokovic welcomed the ongoing 'GOAT' discussion alongside Rafael Nadal and Roger Federer after the world number one took another step towards an historic grand slam title at the US Open.

Djokovic, Nadal and Federer share the most men's slams in history with 20 but the former has the chance to break the record at Flushing Meadows, where the top seed dismantled unheralded Dutchman Tallon Griekspoor 6-2 6-3 6-2 in the second round on Thursday.

Serb star Djokovic is also bidding to become just the third man to complete a calendar Grand Slam and the first to sweep all four majors in a year since Rod Laver in 1969.

It is widely debated who is the greatest player of all time among Djokovic, Nadal and Federer – the latter two are both absent from this year's US Open due to injury.

After reaching the third round in New York, Djokovic was asked who the better player on a neutral surface is, given Nadal's clay-court dominance and Federer's grass-court expertise.

"It's difficult to say who is better. Three of us, we're all so different. We have different styles," Djokovic said during his post-match news conference.

"We have different trajectories or journeys to where we are at this moment. We all had tremendous success, some more particularly on one surface, some the other surface.

"We do complement each other. I think the rivalry between the big three, so to say, it's phenomenal for our sport.

"So the more traction, the more conversation there is around the three of us, the GOAT discussion, et cetera, the better in general for our sport. I hope people still keep on talking about it."

Djokovic added: "I think actually one of the best I think images that I've ever seen from tennis is them [Nadal and Federer] playing on a half-grass, half-clay court.

"I thought that was fantastic. Whoever came up with the idea was genius. As a tennis fan, I enjoyed that very much."

Djokovic hit 33 winners, fired down 13 aces and broke six times throughout a dominant performance against Griekspoor under the Arthur Ashe Stadium lights.

The 34-year-old also improved to 53-1 against non-top 100 opponents at majors, while he is now 13-0 against them at the US Open.

Kei Nishikori awaits Djokovic, who owns a 17-2 head-to-head record against the 2014 US Open runner-up.

"We played many times. I have very good score against him," Djokovic said of Nishikori. "I lost I think last time here in New York in semis in 2014. Historically I think his most successful grand slam is here. He's one of the quickest and most-talented players that I've seen in my lifetime, in my career.

"I think it's important for me to serve well and try to take off the pace a little bit because he likes the pace. He likes to hit the ball early, protect the line. But I know his game well. We played in Olympic Games. I know what's expecting me. I look forward to a good challenge."

Novak Djokovic has history in his sights as he begins his US Open quest; after three grand slam titles in 2021, a fourth beckons at Flushing Meadows.

Rod Laver was the last man to achieve a sweep of the Australian Open, French Open, Wimbledon and US Open singles in the same year, all the way back in 1969.

Steffi Graf won all four on the women's side in 1988, and it seemed a knock-in that Serena Williams would do likewise in 2015 when she headed to the US Open with three majors already bagged.

But winning any title at that level is never easy, and Williams famously came unstuck when she faced Roberta Vinci in the semi-finals.

Djokovic will be mindful that what seems an inevitability to the outside world remains very much still only a possibility. After his US Open tribulations last year, and a recent jolt at the Olympics, he will know anything can happen.

Here, Stats Perform looks at how Djokovic's situation at Flushing Meadows carries most of the hallmarks of Serena's own position as she headed into the tournament six years ago.

IT'S ALL ABOUT THE SLAMS

It was not always this way, but Djokovic has reached the point in his career when he can choose targets, decide which records he wants to break, and throw everything at those goals.

At the start of the year in Australia, he savoured triumphing at Melbourne Park for a ninth time and pointed to how Roger Federer, Rafael Nadal, Williams and Margaret Court had achieved so much.

"They've made history already," Djokovic said. "They made a tremendous mark in our sport. I'm trying to build that and develop that myself in a very unique, authentic way that is suitable to me.

"Whether I think about winning more slams and breaking records, of course. Of course, I do. And most of my attention and my energy from this day forward, until I retire from tennis, is going to be directed in majors, trying to win more major trophies."

It had very clear echoes of Williams in 2015, also in Australia, setting out her own ambitions for the year and specifically targeting the French Open and Wimbledon.

"Those are the two I really have my eye on, because I would like to do better at those. And I know I can do better," she said.

Williams set her heart and mind on that twin challenge and won both.

"I definitely am not going to play as much this year, and I'm just going to go for everything when I do play," said Williams.

BUILDING UP

When Williams reached New York in August 2015, she had delivered a 48-2 win-loss record for the season, landing each of the majors alongside the Miami Open and the Western and Southern Open. Petra Kvitova in Madrid and Belinda Bencic in Toronto had been the only two players to get the better of the 33-year-old Williams.

Djokovic has a 38-5 record for the year, albeit it has the feel of a more dominant year for the 34-year-old Serbian. Two of those losses came at the Olympics, in a semi-final and bronze medal match, and the other three came in his first three events on clay, losing to Dan Evans in Monte Carlo, Aslan Karatsev in Belgrade and Nadal in Rome.

When it mattered on clay, though, Djokovic majorly turned up in Paris, gutsily beating Lorenzo Musetti from two sets down in the fourth round, ending Nadal's streak of four Roland Garros titles by sinking the Spaniard in the semi-finals, and then leaving Stefanos Tsitsipas devastated in the final, with another fightback after dropping the first two sets.

Wimbledon followed, and Djokovic by then was openly targeting a Golden Slam – each major and the Olympic title.

Much like with Williams and her loss to Bencic in the Toronto semi-finals six years ago, however, Djokovic showed he was fallible as history beckoned. From a set up, he lost to Alexander Zverev at Tokyo 2020, a blow that was compounded by missing out on bronze when Pablo Carreno Busta sprang another shock.

HISTORY CAN BE A FIERCE OPPONENT

Williams and Djokovic have won non-calendar Grand Slams before, winning four in succession spanning two seasons.

Williams first achieved that from the French Open in 2002 to the Australian Open in 2003, and in 2015 she was aiming for five slams in a row at the US Open, having begun her dominant streak at her home grand slam the previous year.

She won the first set of the semi-final against Vinci, the world number 43, but was then second best to the Italian, with Williams saying her conqueror "played literally out of her mind".

But the disappointment was stark, underlined by Williams' terse response to the question of how disappointed she felt by the result.

"I don't want to talk about how disappointing it is for me," she said. "If you have any other questions, I'm open for that."

The four-in-a-row feat has only been performed once by Djokovic, from Wimbledon in 2015 to the French Open in 2016. Had he not been disqualified during the US Open last year for carelessly hitting a ball that struck a line judge, he would most likely currently be on a four-slam streak.

Those who win the first three slams of the year often do complete the set, but there are four instances of singles players falling one short by failing in the year's last major.

Before Williams, the most recent case was Martina Navratilova in 1984, when the imperious left-hander headed to the Australian Open – then played at the end of the year rather than the start – in pursuit of the Grand Slam. She lost to Helena Sukova in the semi-finals, and said: "If I'd have won, I'd have done it all. If I lost I had to start from scratch. Both are hard to cope with."

Navratilova had won 74 consecutive matches until that loss and ended the season with a 78-2 record.

In the men's game, Jack Crawford (1933) and Lew Hoad (1956) also fell short, both losing in finals of the US National Championships, the tournament that became the US Open. Don Budge (1938) and Laver (1962 and 1969) are the only men to have won a calendar Grand Slam in singles.

The weight of expectation is immense for Djokovic as he pursues what would be his crowning glory, not only sealing the Grand Slam but reaching 21 majors, one ahead of Nadal and Federer and into the outright lead in the men's game. The prospect cannot be ignored, and it will be a heavy burden to carry over the coming fortnight.

As Djokovic said on Friday: "I would be lying if I said that’s not something that I’m thinking about or that my attention is not going that way.

"I’m very motivated to play my best tennis. But I have to hit one ball at a time, as they say, try to be in the moment, have a guiding star in a way, a dream to win a slam here."

Rafael Nadal was "practically lame" before he called an early end to his season and has been "stumbling all year round", coach Carlos Moya has revealed.

Former world number one and 20-time grand slam winner Nadal will miss the upcoming US Open but hopes to return in 2022, yet Moya says there are question marks over what the best course of treatment will be for the 35-year-old's foot problem.

In announcing his withdrawal from the rest of the campaign, Nadal declared a foot issue that he has been bothered by since 2005 was behind his decision.

The Spaniard took a break after losing a French Open semi-final to Novak Djokovic, skipping Wimbledon and the Olympic Games.

He attempted to make a return for the hard-court season but lost his second match in Washington to South African Lloyd Harris.

Moya, who was also briefly a world number one, said Nadal had managed to prolong a career that was in doubt 16 years ago, thanks to insoles and treatment.

"But this year the story has changed in many training sessions," Moya said. "He could not finish them and we had to change and ease intensity for the foot, thinking about the tournaments.

"He has been in pain for months and there comes a time when he cannot take it anymore. In the last match he played practically lame.

"The best thing was to stop, rest the foot and refresh the head."

Speaking to Spanish broadcaster Onda Cero's El Transistor show, Moya said: "It is not known where this injury comes from. There is a diagnosis but it is not clear which is the best treatment.

"Rafa's main objective is to regain sensations in his feet and in his head, because stumbling all year round has not helped him."

Rafael Nadal has curtailed his 2021 ATP Tour season due to a long-term foot injury but insists he is working towards a return.

Nadal, 35, has played only twice since losing the French Open semi-final to Novak Djokovic in May.

The Spaniard skipped Wimbledon and the Tokyo Olympics and had withdrawn from this week's Western and Southern Open before the US Open.

Nadal will not now compete in the final major of the season either, while great rival Roger Federer is also out for an extended period.

It clears a path for Novak Djokovic – the third man tied on 20 grand slam titles – to win a record-breaking 21st championship at Flushing Meadows while completing a remarkable calendar Grand Slam.

Djokovic could yet have competition again in the years to come, though, as Nadal is not yet calling time on a glittering career.

In making his latest announcement on social media on Friday, Nadal revealed he has been dealing with his injury since 2005 but has not let it halt him yet.

"Hello everyone," he wrote on his Twitter page. "I wanted to inform you that unfortunately I have to end the 2021 season.

"Honestly, I've been suffering a lot more than I should with my foot for a year and I need to take some time.

"After having discussed it with the team and family, this decision has been made and I think it is the way forward to try to recover and recover well.

"It's a year that I've missed things that matter a lot to me, like Wimbledon, like the Olympics, how the US Open is going to be now, like many other events that are also important to me.

"And in view of the fact that during this last year I have not had the ability to train and prepare and compete in the way that I really like to do it, in the end, I come to the conclusion that what I need is time to recover, change a series of things, try to understand what has been the evolution of my foot in recent times.

"It is not a new injury, it is an injury that I have had since 2005 and it has not prevented me from developing my sports career during all these years.

"If it is true that I have had a season where things are not going as they should, as we would all like, it is time to make decisions, seek a slightly different type of treatment to find a solution to this problem or at least improve it in order to continue to have options for the next few years.

"I have the maximum enthusiasm and predisposition to do whatever it takes to recover the best possible form to keep competing for the things that really motivate me and the things that I've done all these years.

"I am convinced that with the recovery of the foot, and obviously a very important daily effort, this can be achieved. I will work as hard as I can to make it happen.

"Thank you in advance for all the support, understanding and all your expressions of affection that are very important and more in difficult times like these.

"I promise you what I am going to do is work hard to try to continue enjoying this sport for a while longer. A big hug to all."

Daniil Medvedev and Stefanos Tsitsipas survived three-set scares at the National Bank Open on Tuesday, but five-time tournament champion Rafael Nadal departed Toronto without even taking the court. 

Top seed Medvedev, who won just three games against Nadal in the final in 2019, the last time the tournament was played, prevailed 4-6 6-3 6-4 in his opener against Alexander Bublik.

The man Nadal beat to win the title the previous year, Tsitsipas, failed to convert on five match points in an epic second-set tiebreak but recovered to down Ugo Humbert 6-3 6-7 (13-15) 6-1.

Nadal pulled out ahead of a scheduled match against Lloyd Harris, who beat him last week in Washington as the 20-time grand slam winner struggled with a foot injury. 

Countryman Feliciano Lopez replaces Nadal in the draw and will face Harris on Wednesday. 

Elsewhere Tuesday, sixth seed Casper Ruud needed more than two hours to put away Marin Cilic 6-3 3-6 6-3, while 14th seed Grigor Dimitrov suffered a quick 6-3 6-4 exit against big-serving American Reilly Opelka.

A pair of unseeded veterans advanced, with 2016 finalist Kei Nishikori a 6-4 6-7 (5-7) 6-2 winner over Miomir Kecmanovic and John Isner defeating Alejandro Davidovich Fokini 6-4 6-1 in just over an hour.

Two days after appearing in his first ATP Tour final at the Citi Open, Mackenzie McDonald fell 6-3 6-4 to Benoit Paire in his Toronto opener. 

In other first-round matches, Karen Khachanov beat Cameron Norrie 6-4 5-7 6-4, Frances Tiafoe downed Yoshihito Nishioka 6-4 6-3, Dusan Lajovic handled Emil Ruusuvuori 3-6 6-3 6-3 and Nikoloz Basilashvili defeated Jenson Brooksby 2-6 6-0 6-4.

Rafael Nadal has withdrawn from the National Bank Open ahead of his opening match due to a left foot injury.

The Spaniard made a return to action on the ATP Tour last week at the Citi Open, his first outing since suffering defeat to Novak Djokovic in the semi-finals of the French Open in June.

His comeback was aimed at getting prepared for the US Open but, having lost in the last 16 in Washington to Lloyd Harris, he will not now be participating in Toronto.

"I really wanted to play here a lot, but now is the moment to make a decision, and this is unfortunately the decision that I have taken," Nadal told the media.

"I have had this issue for a couple of months, as people know.

"Of course, it is not a happy situation after all the success that I had here in Canada, not being able to play this year after missing a year. It's a tough one, but that's how it is today."

Nadal skipped Wimbledon citing the need to recover after the clay season, while the left-hander also opted out of representing his country at the Tokyo Olympics.

The five-time champion in Toronto was scheduled for a repeat meeting with Harris in the second round. Instead, his place in the draw goes to compatriot Feliciano Lopez.

South African Lloyd Harris booked a second-round date with Rafael Nadal at the National Bank Open after a straight-sets win over Canadian qualifier Brayden Schnur on Monday.

World number 49 Harris eased past Ontario-born Schnur 6-3 6-2 in one hour and 17 minutes in Toronto.

Harris sent down nine aces, winning 78 per cent of points on his first serve, converting four from four break points on return.

Nadal is a five-time champion in Toronto, winning the previous two editions in 2018 and 2019.

Marin Cilic, who won his first title for three years in Stuttgart, beat Albert Ramos-Vinolas 6-2 4-6 6-3 in two hours and 13 minutes.

The 32-year-old will face sixth seed Casper Ruud in the next round.

Fabio Fognini also needed three sets to progress, battling from behind to defeat Jan-Lennard Struff 6-7 (2-7) 6-2 6-4 to set up a meeting with Andrey Rublev.

Ugo Humbert impressed in his straight-sets defeat of Lorenzo Sonego and will next face third seed Stefanos Tsitsipas, while qualifier James Duckworth beat Taylor Fritz to secure a showdown with Citi Open winner Jannik Sinner.

Alexander Bublik defeated Briton Dan Evans in straight sets to earn a second round meeting with top seed Daniil Medvedev, while Australian John Millman will face 11th seed Gael Monfils after beating Ricardas Berankis.

Reilly Opelka came from a set down to win over Australian Nick Kyrgios, while Tommy Paul also fought back to beat Canadian Vasek Pospisil.

This time, Rafael Nadal could not summon the third-set magic he needed.

Coming off an epic three-hour duel Wednesday in his first match since the French Open final, Nadal fell to Lloyd Harris 6-4 1-6 6-4 on Thursday at the Citi Open. 

After a short-lived maiden appearance at the Washington, D.C. tournament, the Spaniard will look ahead to Toronto and Cincinnati as he continues his preparations for the U.S. Open. 

Harris, meanwhile, heads to a quarter-final matchup against veteran Kei Nishikori after recording the biggest win of his career. 

Facing Nadal for the first time, the 24-year-old South African slammed 16 aces Thursday and saved four of six break points. 

The 20-time grand slam winner, who battled a foot injury to outlast Jack Sock in his first match, did not have enough to answer the world number 50 on Thursday.

In addition to the top-seeded Nadal's defeat, second seed Felix Auger-Aliassime also went down Thursday, falling 6-3 6-4 to American wild card Jenson Brooksby. 

With their exits, the tournament is now without its top four seeds. 

That leaves fifth seed Jannik Sinner as the top player remaining after he defeated Sebastian Korda 7-6 (7-3) 7-6 (7-3). 

Nishikori advanced by downing seventh seed Cameron Norrie 3-6 6-3 6-3, while John Millman knocked out eighth seed Reilly Opelka 6-3 7-6 (7-4). 

Among unseeded players, Denis Kudla defeated the red-hot Brandon Nakashima 3-6 7-6 (7-3) 6-4, while Steve Johnston eased past Ricardas Berankis 6-2 6-1 and Mackenzie McDonald beat Illya Ivashka 6-4 6-4. 

In addition to Harris-Nishikori, Kudla will face McDonald in the other quarter-final in the top half of the draw, while Sinner meets Johnson and Millman takes on Brooksby in the bottom half. 

World number three Rafael Nadal outlasted Jack Sock in a three-hour epic to progress through to the third round at the Citi Open in Washington D.C. on Wednesday.

The 20-time Grand Slam winner needed a third-set tiebreaker to beat American wildcard Sock 6-2 4-6 7-6 (7-1).

Sock, who is currently ranked 192nd in the world, stormed back into the match with an early break in the second set after the Spaniard cruised in the first.

In a three-hour-and-a-four-minute match which saw only five breaks, Nadal got the edge winning more on his second serve, while he produced some vintage winners too.

Nadal goes through to the third round where he will face 14th seed Lloyd Harris, who progresses after a walkover with Tennys Sandgren retiring mid-match.

Third seed and world number 18 Alex De Minaur was bundled out by world number 81 Steve Johnson 6-7 (5-7) 6-4 6-2.

Fourth seed Grigor Dimitrov also was dumped out with a 6-2 7-6 (7-4) defeat to Belarussian world number 65 Ilya Ivashka.

Sixth seed Dan Evans went out in straight sets to 20-year-old American Brandon Nakashima 7-6 (7-1) 6-0 while 10th seed Taylor Fritz also bowed out to Denis Kudla 6-4 6-2.

Former winner Kei Nishikori knocked off ninth seed Alexander Bublik 6-2 7-5, while 13th seed Benoit Paire lost in three sets to Mackenzie McDonald.

Fifth seed Jannik Sinner got through in straight sets against Emil Ruusuvuori, along with eighth seed Reilly Opelka and 11th seed John Millman.

Young American Jenson Brooksby claimed some revenge for last month's Hall of Fame Open final defeat to Kevin Anderson by beating the South African 7-6 (7-4) 6-3 in the Citi Open first round on Monday.

Brooksby, who received a wildcard for the draw, triumphed in one hour and 49 mnutes against the former world number five.

The 20-year-old American saved a set point at 5-6 in the first set, before winning in a tiebreaker off the back of winning six consecutive points having trailed 1-4.

Former City Open finalist Anderson, who sent down 10-1 aces, had defeated Brooksby to win the Hall of Fame Open last month.

World number 130 Brooksby, who had started the season outside the top 300, claimed the crucial break in the eighth game of the second set.

Brooksby advances to take on American Francis Tiafoe, fresh from competing at Tokyo 2020, as numerous big names enter the draw for the second round.

Kei Nishikori, who won in Washington in 2015, got past American Sam Querrey 6-4 6-3 to set up a second round meeting with Kazakhstani ninth seed Alexander Bublik.

American Jack Sock will take on top seed Rafael Nadal in the second round after he got past Yoshihito Nishioka in a walkover 6-7 (3-7) 4-0.

Former top 20 player Andreas Seppi triumphed in three sets against Yasutaka Uchiyama while Canadian tour veteran Vasek Pospisil got past Emilio Gomez in three.

Ilya Ivashka, Marcos Giron, Ricardas Berankas and Daniel Galan were the other first round winners on Monday.

Novak Djokovic has leapt from one bubble into another as he attempts to become the first man in tennis history to win all four grand slams and Olympic gold in the same year.

The only men to have won each of the singles majors across their careers, plus Olympic gold, are Andre Agassi and Rafael Nadal, and now Djokovic aims to move to the brink of winning all five in his remarkable 2021 season.

Fresh from dominating at Wimbledon, and with the Australian and French Open titles already in the bag, Djokovic heads into the Tokyo Games as a red-hot favourite, seeking to set himself up to complete a historic campaign at the US Open.

Naomi Osaka will enter the Games with almost as much expectation behind her too, the reigning US Open and Australian Open champion eyeing glory for hosts Japan.

But tennis has thrown up a host of shock results in its short Olympic history. Here, Stats Perform looks at the sport's place in the Games.

WHO'S IN, WHO'S OUT, AND WHAT DOES ALL THIS MEAN?

Serena Williams, Roger Federer and Rafael Nadal have all opted out of the Olympics.

Williams made her mind up prior to suffering a leg injury at Wimbledon, although she is already a member of the career Golden Slam club.

Federer reached his decision after revealing he also suffered a physical setback at the All England Club, and Nadal elected to take a two-month break after relinquishing his French Open title.

Don't expect to see them again at the Olympics, given Williams and Federer will be pushing 43 by Paris 2024, and Nadal will be 38. Federer won a doubles gold with Stan Wawrinka in 2008, but his singles peak was the silver medal he earned in 2012, Andy Murray crushing Swiss hopes in the final at Wimbledon.

Dominic Thiem, Bianca Andreescu, Nick Kyrgios, Simona Halep, Angelique Kerber, Victoria Azarenka and Denis Shapovalov are among other confirmed absentees, with fitness issues a factor for some, less so for others.

The COVID-19 crisis is a mitigating factor in why so many stars are staying away, and directly responsible in the case of some players, such as Britain's Johanna Konta and Dan Evans, who both tested positive recently.

But tennis was only fully restored to the Olympic programme in 1988, after being dropped post 1924, and if players are seen to be favouring the grand slams over the Games, that is not such a great look for the sport.

At a time when the International Olympic Committee has shown it is willing to shake up the sports on its programme, tennis could perhaps do with a headline-making Tokyo 2020.

Murray, the two-time defending men's champion, will target an improbable hat-trick. A hat-trick for the injury-hit former world number one would be a sensation, and Osaka landing gold in the women's tournament would surely be one of the great moments of the Games.

DJOKOVIC FOLLOWING IN THE FOOTSTEPS OF GRAF

When Steffi Graf beat Gabriela Sabatini in the women's singles final at Seoul, it completed what we know now as the calendar 'Golden Slam'. She had already won the Australian Open, French Open, Wimbledon and the US Open, and the feat of the then 19-year-old West German has yet to be repeated.

Now Djokovic is three-fifths of the way to a similar clean sweep of the majors and the Olympics, with the US Open getting under way on August 30 in New York.

He teetered on not going to Tokyo, and perhaps he is to some extent endangering his chances at Flushing Meadows by spending more time travelling and enduring bubble life, while others rest up.

But Djokovic is a fiercely proud Serbian and could not resist a great chance of winning gold for his country. He landed bronze at the 2008 Games in Beijing but in 2012 he lost to Juan Martin del Potro in the bronze-medal match, and a cruel draw at Rio four years later saw him assigned Del Potro in the first round.

Top seed Djokovic bowed out in two tie-breaks to the powerful Argentinian, describing the outcome as "one of the toughest losses in my career".

There is no danger of a hat-trick of defeats to Del Potro, which may help Djokovic. Del Potro has been battling for two years to get back to fitness, undergoing four rounds of right knee surgery in a bid to get back on tour.

RAISING THE BAR AT THE OLYMPICS

How the Olympic village functions in Tokyo will be distinctly different to at previous Games, given the pandemic restrictions in place that could be a real buzzkill.

But in the past there have been countless cases of athletes becoming inspired by their surroundings and going on to perform above their usual level.

It can be a party village, and it can also be an eyebrow-raising experience as global superstars rub shoulders with competitors who might struggle for recognition in their home towns. More than anything, the shared team experience, fighting for a collective cause, can make a middling athlete believe they can be great.

Monica Puig was a massive tennis outsider in 2016 but the then world number 34 won the women's singles, stunning Angelique Kerber in the final after beating Petra Kvitova and Garbine Muguruza en route. That gave Puerto Rico their first ever Olympic gold medal.

In 1992, a tournament that featured the likes of Pete Sampras, Jim Courier, Stefan Edberg and Boris Becker finished with a staggering final match-up of Marc Rosset versus Jordi Arrese, who in his home city of Barcelona was edged out 8-6 in the fifth set by the Swiss world number 43. Nobody would have predicted that head to head for gold.

Similarly, at Athens 2004, Nicolas Massu beat Mardy Fish in the gold medal match of a tournament that featured Federer, Andy Roddick, Carlos Moya and Tim Henman.

In the 1996 Atlanta Games, Lindsay Davenport, who had just turned 20, took inspiration from being the daughter of an Olympian, with dad Wink having played volleyball for the United States at Mexico City in 1968.

Davenport was beginning to make an impact on the WTA Tour but was only the ninth seed at the Olympics, yet she swept through the rounds before sinking Arantxa Sanchez Vicario 7-6 (10-8) 6-2 in the final.

"It's like one of those things I look back on and I'm like, 'Was that me?'," Davenport told The Tennis Podcast last year.

"It doesn't seem like it was real. I'd made the transition to the pro tour pretty well, but I liked hanging out between eight and 16 in the rankings. I was very insecure, unsure of what could I do. I liked doing well but I wasn't sure I wanted to do too well because it seemed really overwhelming to be one of those top players.

"Here I go at 20 years old to Atlanta for two or three weeks, in a setting that seemed so comfortable. Look at all these athletes, you have all different shapes and sizes, you have players that are really working hard but have so much in common and you get to hang out with them, breakfast, lunch, dinner in the village."

Davenport was a future world number one and three-time grand slam singles champion, but at this point in her career being an American at an Olympics in the United States was just a thrill.

"You're sharing this with your team-mates who are some of my best friends in Mary Joe Fernandez, Monica Seles. It was the best time ever," she said.

"By the time the tournament actually started we were like, 'Yeah, I'll go play my match and then we'll go back to the village and we'll hang out', and everything went so fast in those few weeks.

"And there I was left standing, winning at the end because I was so incredibly happy and excited with everything that was going on. I kind of forgot what was my job.

"When it became a reality of even just making the team in '96, it was so huge also for my family with having a second generation Olympian."

Novak Djokovic will never have a better opportunity to achieve a historic calendar Grand Slam, which former Wimbledon champion Pat Cash says he should prioritise at all costs.

The Serbian won a sixth Wimbledon crown on Sunday, defeating Matteo Berrettini in four sets to achieve a final victory that moved him on to 20 grand slam titles.

With Australian Open and French Open successes also already achieved, glory at the US Open would see Djokovic become only the second men's player in Open Era history to win all four majors in the same year.

Cash thinks the stars have aligned for Djokovic, with issues for his main rivals leaving the 34-year-old primed to achieve the famous feat in 2021.

"The impossible dream really is there," Cash said to Stats Perform.

"For Novak this year it is a great opportunity for him to grab a bunch of grand slams and grab all the titles. 

"Certainly Wimbledon – without disrespecting the other players – was one of the weaker men's side draws that I've seen in many, many years. 

"And that's because we've got two of the big stars coming back from injuries – Andy Murray and Roger Federer – who played well but weren't at the peak of their career.

"The younger players are coming through but they're not quite there yet and Novak is just sitting on top of that mountain as the King of the Castle.

"His performance was exceptional at Wimbledon, there's no doubts about it. 

"The slightly younger players are coming through – Berrettini obviously in the final really pushed him to just about the limit.

"Stefanos Tsitsipas in the French Open final up two sets to love. So, these guys are close, very close, and it won't be long before they catch up with Novak and the others. 

"Obviously Rafa [Nadal] was out of this Wimbledon as well – I don't really think he's a serious threat on the grass anymore but he's still a great competitor. 

"So these guys are catching up, Rafa is still there, maybe Murray will come back and Federer will come back and be in better shape in the next year – but this is the year that Novak can really grab." 

Djokovic admitted this week he is still "50/50" over whether he will take part in the upcoming Tokyo Olympics due to coronavirus countermeasures in the Japanese capital. 

Federer withdrew from the tournament on Tuesday and Cash insists Tokyo will not be the priority over glory in New York for Djokovic.

Cash added: "It's the Olympics, okay – maybe he wants to do that, but certainly his goal is now to try and win all four grand slams in the calendar year.

"He has done four in a row, but he hasn't done them in the same year, which is very, very tough to do. 

"There is a reason why I think one person has done it in [men's] professional tennis – Rod Laver and it was in 1969, so it's not easy to do. 

"But I really do think it's in his sights and that has got to be his priority. 

"It's absolutely the absolute peak of our sport to win all four grand slams in one year." 

With Djokovic now level with Federer and Nadal on 20 majors, Cash would not be surprised to see him build a big lead.

He added: "Look, it's very hard to say. We have all been proven wrong by the numbers. 

"Though most of us thought that Rafa and Novak would get pretty close to Federer, we didn't really think they'd get there and beyond. 

"I think Novak is likely to win another couple, but you know, it takes us one little injury [to derail him] so it is very hard to say.

"John McEnroe said 25 or so [for Djokovic] and that could be well within his reach at the moment. 

"He's improving and that's frightening to think. He's won 19 grand slams before Wimbledon, and all of a sudden we've seen this guy come to the net, volley, add another string to his bow to become a better player. 

"Yeah, age 34 and he is improving – that's pretty frightening." 

Roger Federer is proud to play in an era of tennis which he labelled as "special" after Novak Djokovic clinched his 20th grand slam title.

Djokovic beat Matteo Berrettini 6-7 (4-7) 6-4 6-4 6-3 at Wimbledon on Sunday to seal his third major trophy of the season.

It is the world number one's sixth title at the All England Club, as he defended the crown he won in an epic final against Federer in 2019.

Djokovic is now level in the record books with Nadal and Federer, with all three of the greats on 20 grand slams each.

The Serbian will look to make that 21 at Flushing Meadows later this year, as he aims to become just the second player in the Open Era to complete a clean sweep of the men's slams in a single year, after Rod Laver in 1969.

In the post-match presentation, Djokovic hailed Nadal and Federer as inspirations, and the latter echoed that sentiment.

"Congrats Novak on your 20th major," Federer, now ranked eighth in the world, tweeted.

"I'm proud to have the opportunity to play in a special era of tennis champions. Wonderful performance, well done!"