Alexander Zverev believes world number one Novak Djokovic remains the favourite for the upcoming U.S. Open despite the German backing up his Olympic gold medal with victory in Cincinnati.

The German world number four defeated Andrey Rublev in straight sets on Sunday to win the Western and Southern Open, claiming his fourth title of the ATP season.

The 2021 U.S. Open begins next Monday with Dominic Thiem, who defeated Zverev in the 2020 final, withdrawing from the men's draw along with superstar Roger Federer and Rafael Nadal.

Their absences have opened up an opportunity for the in-form Zverev to have a run at the title but the German insisted Djokovic, who he defeated in the Olympic semi-finals, is the player to beat.

"I do think that he's still the favourite," Zverev told reporters after his win in Cincinnati.

"I do think he's going to be playing incredible tennis there. He's going to be fresh, and I think there is also other guys that are in very good form. I think Rublev is in very good form, [Daniil] Medvedev, [Stefanos] Tsitsipas, all those guys are playing great tennis.

"It's definitely going to be an interesting US Open. But I'm also looking forward to it, because I know where I stand, I know how I'm playing, and I hope I can continue the work and hopefully play even better in New York."

Djokovic has not played since Tokyo 2020, where he lost his bronze medal match to Pablo Carreno Busta after his semi-final defeat to Zverev.

The Serbian world number one opted to withdraw from the mixed doubles' semi-final afterwards, citing a left shoulder injury.

"I think Novak will be back. He's obviously going to be the favourite but I think other guys are going to be in great shape,” Zverev said.

"I'm looking forward to the week. Let's see how it goes. But there is still one week to go. I still have a lot of work ahead of me. I have to find my rhythm in New York, as well."

Zverev, who had never won a match in Cincinnati prior to this year's event, has not lost a match since his Wimbledon fourth-round exit to Felix Auger-Aliassime in July.

Alexander Zverev claimed his fourth title of 2021 with a 6-2 6-3 victory over Andrey Rublev to win the Western and Southern Open.

The Olympic champion had not won a match in Cincinnati prior to this year's tournament, but Sunday's one-sided final capped a remarkable turnaround for the world number five.

Zverev raced into a 4-0 lead before securing the opening set 6-2 as he produced no errors across the first seven games.

The third seed carried on his domination, breaking Rublev in his opening service game of the second set to pave the way for the 17th ATP title of his career within an hour in the showpiece.

After paying tribute to "his best friend on Tour" Rublev, Zverev added in his on-court interview: "It is incredible that tennis can be back, sport can be back, and we can watch and play this beautiful sport again.

"I normally do not look forward to this week - not winning a single match in seven years - but this has now become one of my favourite times of the year for me, hopefully it can be for the next 10 to 15 years."

The 24-year-old reached the final of the US Open last year, though he will now eye going one step further as the tournament commences at the end of August.

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."

Andrey Rublev finally got the better of compatriot Daniil Medvedev after a flashpoint involving a courtside camera in the Western and Southern Open semi-finals.

Rublev will now face Alexander Zverev in the decider, having ended Medvedev's bid for a Toronto-Cincinnati double.

Medvedev had never even dropped a set to his fellow Russian in four prior ATP Tour meetings and appeared to be on course for another dominant victory when he took the first set.

But the world number two clattered into a camera early in the second and all momentum was soon lost.

Medvedev complained about the positioning of the camera, claiming it had caused a hand injury and aiming a kick at the lens.

He swiftly called for treatment as his performance started to fall well below his lofty standards, with Rublev finally able to win a set after breaking in an epic 15-minute game.

A series of unforced Medvedev errors allowed Rublev to break again in the decider and seal a stunning 2-6 6-3 6-3 triumph.

Third seed Zverev fought back from a double break down in the final set to progress to the final with a 6-4 3-6 7-6 (7-4) win over second seed Stefanos Tsitsipas.

The epic match lasted two hours and 41 minutes, with Zverev responding strongly after appearing unwell to book his spot in the final against Rublev.

Rublev gets his Daniil degree

Asked to reflect on finally toppling Medvedev, Rublev told Amazon: "It's always tough to play against Daniil and to beat him.

"I think it gives me a bit more confidence that I can play against him, I can compete against him. There are still so many things to improve, but it's like I've passed university."

The victory came as a relief, with Rublev believing he was unfortunate even to be trailing in the first set.

"Inside I was thinking, when I was 6-2, the score shouldn't be like this," he said.

"The points were really tight, some little outs, little mistakes, some good shots from Daniil. The score was not real [in] the first set.

"Even the third set, I won 6-3 but the match was so intense. You saw so many rallies, so many long rallies, and it was so tough.

"It was a super mental match, a super physical match, exactly like a chess match."

Zverev's Novak mentality

Tokyo 2020 gold medalist Zverev had trailed 4-1 in the third set against Tsitsipas, but fought back with two breaks before winning in a tie-break.

"After I did the first break back I thought 'OK I have the chances'," Zverev said during his on-court interview. "I felt like he was not serving bombs. I felt like I was always in the rallies but I was losing the rallies because I was a bit low energy, so I started being a bit more aggressive, a bit of the Novak mentality that I had against him at the Olympics as well."

Zverev has a 4-0 record against final opponent Rublev but he was wary of his opponent.

"Favourite or not, I think if you're in the final, there's no easy opponent," he said. "Today he played incredible beating Medvedev."

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."

Defending US Open champion Dominic Thiem will miss this year's tournament with a wrist injury that will rule him out until 2022.

The 27-year-old suffered the setback at the Mallorca Open in June and also withdrew from Wimbledon and the Tokyo Olympics.

World number six Thiem won his maiden grand slam at Flushing Meadows last year with victory over Alexander Zverev in a five-set thriller, but he will not get the chance to defend his title in New York.

"Having spent a week training on court, I still felt pain in my wrist and I knew that it was not 100 per cent," Thiem posted in a statement on his Twitter page on Wednesday.

"I went to see my doctors again and we have decided to follow a conservative treatment, giving the injury more time to recover.

"I'm very disappointed not to be able to defend my US Open title and to miss the rest of the season.

"But I know this is what I have to do. I have a long career ahead of me, so I will only come back once I'm fully recovered and in good shape to compete."

Thiem has a record of nine wins and nine losses this season, with his best result coming at the Madrid Open in May when reaching the semi-finals.

Twenty-time grand slam winner Roger Federer last week pulled out of the US Open, which runs from August 30 until September 12, after undergoing knee surgery.

Fifth seed Matteo Berrettini survived an early scare on his return from a thigh injury to progress in the second round of the Western and Southern Open in Cincinnati over Albert Ramos-Vinolas on Tuesday.

The Italian world number eight, making his ATP Tour return since losing the Wimbledon final to Novak Djokovic in July, won 6-7 (5-7) 6-3 7-5.

The Spaniard claimed the first set in a tie-break but Berrettini hit back, sending down 25 aces for the match, winning 84 per cent on his first serve.

"I'm happy for the win. I think I served really well," Berrettini said. "My strokes from the baseline weren't working the way I wanted them to, but I knew from the beginning it's been a long time since I played a match, especially on hard, so I expected to feel a little bit weird."

The match extended to two hours and 20 minutes, with the Italian utilizing his backhand slice in the final set to get the edge.

Berrettini, who has a 33-7 record for the season, will face 12th seed Felix Auger-Aliassime or Karen Khachanov in the third round.

"I'm really happy that I'm going to have the chance to play another match because that's what I need," Berrettini said. "I need to play matches. I need to get in the best shape possible."

Canadian sixth seed Denis Shapovalov suffered a shock early upset, going down to France's Benoit Paire 6-3 4-6 7-5 in the Round of 64.

Former US Open, Wimbledon and Australian Open semi-finalist Grigor Dimitrov toppled 13th seed Roberto Bautista Agut 6-3 6-4 in one hour and 21 minutes.

Fellow seed Cristian Garin also bowed out, losing 4-6 6-3 6-4 to qualifier Tommy Paul, while ninth seed Hubert Hurkacz defeated Alejandro Davidovich Fokina 6-1 6-7 (3-7) 6-1.

Marin Cilic, John Isner, Sebastian Korda, Gael Monfils, Reilly Opelka, Lorenzo Sonego and Frances Tiafoe were the other Tuesday winners.

Isner sent down his 13,000th career ace in his three-set win over Briton Cam Norrie.

Stefanos Tsitsipas has indicated he will only get the COVID-19 vaccine if it becomes mandatory to participate on the ATP Tour.

World number three Tsitsipas revealed he has not yet been jabbed against coronavirus with the tennis world divided on the issue. 

The ATP Tour have publicly encouraged players to get vaccinated, but Novak Djokovic is among the high-profile players to have stated it should not be compulsory to compete.

When asked ahead of the Western and Southern Open if he would get the vaccine, Tsitsipas told a media conference he still had reservations.

"No one has told me anything. No one has made it a mandatory thing to be vaccinated," the Greek said.

"At some point I may have to, I'm pretty sure about it, but so far it hasn't been mandatory to compete, so I haven't done it, no."

Tsitsipas received a bye through to the second round in Cincinnati, where he will play either Sebastian Korda or Laslo Dere.

The 23-year-old, who has a tour-high 45 wins this season, climbed up to third in the world rankings last week and boldly targeted overhauling Djokovic in top spot.

"The rankings are there for a reason. They signify something important," he added.

"I think that the very next step would be the number one spot, which I hope I can get to one day.”

Andy Murray looked sharp in his first singles match since Wimbledon, rolling to a straight-sets win over Richard Gasquet at the Western and Southern Open. 

Murray defeated the veteran Frenchman 6-4 6-4 on a rainy opening day in Cincinnati, capitalising on a strong service game to advance. 

Murray had 14 aces to just two double faults and won 81 per cent of points on his first serve while saving four of the five break points he faced. 

A two-time champion at the ATP 1000 event, he will face the winner of Tuesday's match between Alejandro Davidovich Fokina and ninth seed Hubert Hurkacz in the second round. 

Two players who shared a birthday Monday also prevailed on their big day. 

On the day he turned 20, 11th seed Jannik Sinner defeated Federico Delbonis 6-2 7-5, while 10th seed Diego Schwartzman had to work a bit harder on his 28th birthday to down Daneil Evans 6-2 4-6 6-3. 

Elsewhere, 12th seed Felix Auger-Aliassime beat Marton Fucsovics 7-6 (7-0) 6-3, while 14th seed Alex de Minaur rallied to down Filip Krajinovic 0-6 6-4 6-4. 

Fifteenth seed David Goffin fell 6-3 6-3 to Guido Pella in the only seeded upset of the day. 

Other winners Monday included Karen Khachanov, Fabio Fognini, Lloyd Harris, Dominik Koepfer, Benoit Paire, Albert Ramos Vinolas and Mackenzie McDonald. 

Among those set to play their opening matches Tuesday are third seed Alexander Zverev, who will face Harris, and sixth seed Denis Shapovalov, who plays Paire. 

Daniil Medvedev lived up to his top-seed billing by overcoming Reilly Opelka in straight sets in the National Bank Open final.

World number two Medvedev prevailed 6-4 6-3 in Toronto on Sunday as he became the first Russian to win the ATP tournament since Marat Safin in 2000.

Medvedev now holds four of the nine ATP Masters 1000 titles, having also previously come out on top in Cincinnati, Shanghai and Paris.

He saved all four break points faced against unseeded Opelka, who stunned Stefanos Tsitsipas in the semi-finals, and needed just 85 minutes to complete the job.

Reflecting on his latest tour triumph, Medvedev said: "I could not have dreamt of this at one point.

"With Novak [Djokovic] and Rafael [Nadal] playing, it seemed like an untouchable achievement. Now I have four wins in five finals, which is a good score. I am just happy. 

"Playing Canada and Cincinnati, the goal is to win as many matches as possible. I was able to do it two years ago and I will try and do it again."

Opelka was competing in his maiden final at this level and started strongly, racing 40-0 ahead in the fourth game with some powerful hitting.

However, the 23-year-old – the first American to reach the final since Mardy Fish in 2011 – could not break his opponent as Medvedev recovered with some impressive serving to take the game.

Medvedev earned the first break in the following game and comfortably held to take the first set.

The Russian forced Opelka into errors in the second set and reeled off nine points in a row en route to breaking his opponent in the third game.

It was plain sailing from that point on as two-time beaten grand slam finalist Medvedev eased over the line to add another trophy to his collection.

Roger Federer will not take part in the upcoming US Open after the 20-time grand slam winner announced he is to undergo knee surgery that will rule him out for "many months".

The 40-year-old has not been in action since losing to Hubert Hurkacz in a Wimbledon quarter-final in July and has completed only five events this year.

Federer underwent two operations on his right knee in 2020 and requires another procedure that the legendary Swiss hopes will give him a chance to return to the court.

"I just wanted to give you a bit of an update on what's been going on since Wimbledon," Federer, who won the most recent of his five titles at Flushing Meadows in 2008, posted in a video message on his Instagram page on Sunday.

"As you can imagine, it's not been simple. I've been doing a lot of checks with the doctors as well on my knee, getting all the information as I hurt myself further during the grass-court season and Wimbledon.

"That's just not the way to go forward, so unfortunately they told me for the medium to long term to feel better, I will need surgery. I decided to do it.

"I'll be on crutches for many weeks and also out of the game for many months, so it's going to be difficult of course in some ways.

"But at the same time I know it's the right thing to do because I want to be healthy, I want to be running around later as well again and I want to give myself a glimmer of hope to return to the tour in some shape or form."

Federer, now ranked number nine in the world, missed more than a year of action after first having his knee operated on shortly after the 2020 Australian Open.

"I am realistic, don't get me wrong," he said. "I know how difficult it is at this age right now to do another surgery and try it. 

"But I want to be healthy, I will go through the rehab process I think also with a goal while I'm still active, which I think is going to help me during this long period of time."

Federer added: "Also a big thank you already now for all of your messages that are going to be coming in because you guys are always incredible. 

"You always think of me. Some of you suffer with me. I'll update you as I move along with my rehab. I wish you all the best and I'll check in with you soon."

The US Open in New York begins on August 30, with Dominic Thiem looking to retain his title.