Roger Federer believes the intense tennis tour schedule can have a negative impact on the mental health of players.

Federer, now retired, won 20 grand slam titles between 2003 and 2018 before stepping away from the sport in September of this year, and he is well aware of the challenges players face.

A number of big-name stars have spoken out about their mental health, including Naomi Osaka and Nick Kyrgios, and Federer feels the packed tennis calendar does not help players.

"When players retire at a super young age, I totally understand it," Federer told a press conference in Tokyo. "The tour is tough... travel, practice, jetlag.

"Nobody is allowed to say, 'Oh, I'm tired today', because it looks like you're weak, and that's why players end up having sometimes mental problems.

"You're supposed to show strength. But we're also not machines, we’re also just human beings."

Federer played on the tour for 25 years before calling it a day, and he is making the most of being able to finally relax, saying: "As a tennis player you're always thinking about your next practice, your next match. It never lets you go.

"I don't think I was that much aware of it, how much that thought is always there, and it rides with you, until you retire and then you realise that stress all drops away."

He pointed to doping tests, and the fact players must constantly make authorities away of their whereabouts.

"We have to fill out the doping forms every single day, one hour during the day, where you are," Federer said. "You're always aware in the back of your head, they could be coming any moment, especially in that hour.

"Once that all drops away you actually feel quite lighter, relieved that you can actually live normally again after 25 years."

Naomi Osaka's title defence at her home Pan Pacific Open event came to a premature end as she withdrew from her second-round match against Beatriz Haddad Maia.

The former world number one, who won the Tokyo tournament when it was last held in 2019, was unable to compete in Thursday's match due to illness.

"I am really sorry that I am not able to compete today," Osaka said. "It's an honour to be able to play at the Pan Pacific Open in front of the amazing fans here in Japan.

"This has and always will be a special tournament for me and I wish I could have stepped on court today, but my body won't let me."

Haddad Maia advanced on a walkover and will next face fourth seed Veronika Kudermetova, who defeated Mexican qualifier Fernanda Contreras Gomez 6-0 6-1 to reach the quarter-finals.

Liudmila Samsonova also progressed to the last eight, with a 7-6 (7-5) 6-3 win over Wang Xinyu continuing her good form.

However, sixth seed Karolina Pliskova exited the competition on Thursday at the hands of Petra Martic, who prevailed 6-3 6-4 and will face Zhang Shuai next.

At the Korea Open, top seed Jelena Ostapenko recovered from two games down in the deciding set to overcome Anastasia Gasanova 6-3 5-7 7-5.

Ostapenko remains on a possible semi-final collision course with Emma Raducanu, who came through 6-4 7-5 against Yanina Wickmayer, while Magda Linette saved two match points to beat Kristina Mladenovic 4-6 7-6 (7-5) 6-2.

Naomi Osaka began the defence of her Pan Pacific Open crown with a quick win after opponent Daria Saville was forced to retire in just the second game.

Four-time grand slam champion Osaka won the opening game, before Saville was unable to continue due to a scary-looking injury to her left knee.

The former world number one will now face a second round match with world number 16 Beatriz Haddad Maia, who eased to a straight sets victory over Yuki Naito.

Karolina Pliskova secured her place in the next round in Tokyo with a 6-2 6-1 demolition of Isabella Shinikova, while Zhang Shuai will face second seed Caroline Garcia on Wednesday after overcoming Mai Hontama in two sets.

In Seoul, Jelena Ostapenko's hopes of repeating her 2017 heroics at the Korea Open are still alive after the number one seed narrowly beat 19-year-old Jeong Bo-young.

The world number 19 looked to be cruising after the opening set, but the unheralded South Korean hit back in the second and took it to a tie-break in the third, before Ostapenko's class showed as she won the crucial tie-break 7-2.

Elsewhere, 2021's beaten finalist Kristina Mladenovic saw off wildcard Park So-hyun 6-4 4-6 6-3, while second seed Ekaterina Alexandrova overcame a worrying second set to beat Asia Muhammad 6-1 3-6 6-1.

Wimbledon semi-finalist Tatjana Maria is also safely through to the second round after a tight 7-6 (7-5) 7-6 (7-5) triumph over Eugenie Bouchard.

Four-time grand slam champion Naomi Osaka admitted she has not had "the best year" but is still "pretty happy with where I am now."

Osaka – a former world number one – has slipped to 48th in the latest WTA rankings, and has not won a match at a grand slam since she beat Madison Brengle in the second round at the Australian Open in January.

The Japanese-born star was eliminated in the first round at the French Open and US Open this year, and did not compete at Wimbledon due to an Achilles injury.

Having taken some time away from the game last year to focus on her mental health, Osaka has struggled to get back to her previous high levels.

However, speaking ahead of the Pan Pacific Open in Tokyo, she seemed calm about the situation, as she suggested she is improving both on and off the court.

"It was kind of hard at first, just because I feel like I should be somewhere where I'm obviously currently not," the 24-year-old said.

"I think for me, it's more about being at peace with myself. I know that I'm here for a reason."

Osaka has seven career singles titles to her name, including four majors – she has won twice at Flushing Meadows and twice at the Australian Open.

"This year has not been the best year for me, but I've learned a lot about myself," she added.

"Life is ups and downs, and this year was more down than up, but overall I'm pretty happy with where I am now."

She is preparing to defend her title at the Pan Pacific Open, which has not been held in three years due to the coronavirus pandemic, starting with a match against Daria Saville on Tuesday.

"It feels really weird to hear that I'm the defending champion because it was the last time I played in 2019," she said.

"I would love to win it again, but I think just taking it one match at a time... and also just playing in front of a crowd in Tokyo again, because the Olympics was crowdless, so it will just be nice to see people."

Naomi Osaka suffered another early major exit at the US Open on Tuesday and reflected on a difficult season.

Osaka is a four-time grand slam champion, winning twice at Flushing Meadows in 2018 and 2020.

However, the former world number one has not been able to contend in 2022, winning only two matches at majors – both at the Australian Open.

In fact, Osaka has not been beyond the third round at a slam since her most recent title in Melbourne at the start of 2021.

Tuesday's 7-6 (7-5) 6-3 defeat to Danielle Collins was just the 22nd Tour-level match Osaka has played this year.

"This year hasn't really been a great year," she said, adding: "I feel like everyone deals with injuries. I would say, for me, it's been more prominent this year.

"But I think it's something that I can learn [from]. I learned a lot more about my body, I learned what's weak, what I can do to prevent it.

"I would say the sport is definitely very physical, but it's my job to stay on top of it."

Given her fitness troubles, Osaka was just relieved to be able to play a competitive match against Collins, even if it was a fourth defeat in a row – her worst run since 2018.

"Honestly, the main goal was just to have fun," she said. "I don't know. I think that was kind of accomplished.

"Of course, it's more fun to win more rounds. We're just kind of winging it."

Naomi Osaka's difficult run of form continued in the opening round of the US Open on Tuesday, going down against Danielle Collins 7-6 (7-5) 6-3 in the final match of the night.

Osaka was the unseeded party as she went up against the world number 19, but she appeared to have things clicking early as she collected an early break of serve to rattle off the first three games of the match.

But as would be a theme in the back-and-forth contest, Collins fought right back, taking the next three games to even things up.

Collins' serve was not sharp throughout the clash – committing all nine of the match's double faults – but she found a couple of crucial first serves in the tiebreaker to come away with the first set.

Just like the first set, it was Osaka nabbing the early break in the second, but that advantage was again wiped out instantly as Collins fought back to level, before breaking again to go up 5-3 with a chance to serve it out.

Osaka had two break points in the final game, but could not extend the contest as Collins saved five out of six break opportunities in the second set, while taking two of her three chances.

Data Slam: Osaka's yearly grand slam streak comes to an end

This will be the first year since 2017 that Osaka has not won a grand slam, after her two Australian Open victories in 2019 and 2021 and two US Open crowns in 2018 and 2020.

She has now lost four matches in a row for the first time since 2018, and six of her past seven.

WINNERS/UNFORCED ERRORS

Osaka – 25/19

Collins – 23/24

ACES/DOUBLE FAULTS

Osaka – 8/0

Collins – 1/9

BREAK POINTS WON

Osaka – 2/8

Collins – 3/5

Coco Gauff shined on the opening day of the Canadian Open on Tuesday, defeating American compatriot Madison Brengle 6-1 6-3 to move to a record of 14-4 from her past 18 matches.

Gauff, who has not lost to anyone ranked lower than world number 22 Amanda Anisimova since the Australian Open, continued that impressive record by cruising past world number 62 Brengle, winning 58 per cent (34-of-59) of her return points in a dominant showing.

Anisimova, who eliminated Gauff from Wimbledon, also made it through her first match unscathed as she defeated hometown Canadian Carol Zhao 6-1 6-3.

China's Qinweng Zheng put another dagger into the Canadians with her 3-6 7-6 (7-5) 6-4 win over Rebecca Marino, but Bianca Andreescu gave the fans something to cheer for as she upset world number nine and winner of this past week's Silicon Valley Classic Daria Kasatkina 7-6 (7-5) 6-4.

Spain's Sara Sorribes Tormo prevailed against American Claire Liu 7-6 (7-4) 2-6 7-6 (7-5) in a three-and-a-half-hour battle of attrition, while Australian qualifier Ajla Tomljanovic upset world number 16 Veronika Kudermetova 6-4 2-6 7-6 (7-4) in two-and-a-half hours.

It was a disappointing showing from world number 10 Emma Raducanu as she went down 7-6 (7-0) 6-2 to the reigning champion of this event, Italy's Camila Giorgi.

Naomi Osaka also will need an early flight home after being forced to retire against Estonia's Kaia Kanepi, pulling the plug due to a persistent back injury while trailing 7-6 (7-4) 3-0.

In the late session, Olympic gold medalist Belinda Bencic successfully navigated the challenge of Tereza Martincova 6-4 6-2 to book a second round fixture against Serena Williams, and world number four Maria Sakkari survived a scare to finish strong and defeat Sloane Stephens 6-2 4-6 6-2.

Coco Gauff was too sharp with her return game for Naomi Osaka in the second round of the Silicon Valley Classic on Thursday, coming away with a 6-4 6-4 win.

Gauff – the world number 11 and tournament's sixth seed – created 12 break point opportunities in the match, while only allowing one for Osaka, despite eight double-faults.

Ultimately, Gauff won 41 per cent (29-of-71) of the points off Osaka's serve, while converting 85 per cent (28-of-33) of her successful first serves into points.

Earlier in the day in a major upset, top seed Maria Sakkari was eliminated in straight sets 6-1 6-3 by American Shelby Rogers. 

The world number three struggled with her serve throughout, landing only 45 per cent of her first serves, and winning just 52 per cent (12-of-23) of those points.

World number six Aryna Sabalenka needed three sets to defeat unseeded American Carolina Dolehide 5-7 6-1 7-5, and Russia's Veronika Kudermetova had less trouble dispatching Claire Liu 6-2 7-5 to set up an exciting match with Ons Jabeur in the quarter-final.

Meanwhile, in Washington at the Citi Open, Emma Raducanu played in the longest two-set match of the WTA season, defeating Camila Osorio 7-6 (7-5) 7-6 (7-4) in two hours and 49 minutes.

Both women created at least a dozen break point opportunities, with four total breaks each as the young British star battled blisters on her hands.

Raducanu will play Liudmila Samsonova after the Russian eliminated Australia's Ajla Tomljanovich 4-6 6-3 6-2.

In the last match of the day, China's Xiyu Wang got the better of Croatia's Donna Vekic 4-6 7-5 6-1, and she will meet the winner between Tereza Martincova and Victoria Azarenka in the quarter-final.

Naomi Osaka delivered a terrific third set to defeat China's Qinweng Zheng 6-4 3-6 6-1 in the opening round of the Silicon Valley Classic.

Osaka's serve was sharp and it carried her through the match, with 11 aces to Zheng's three, while giving up one break of serve and securing three breaks herself.

After Zheng fought back to win the second set, Osaka was the steady head in the decider, allowing her opponent to implode with three double-faults in crucial points to collect her first win since April.

Osaka will meet Cori Gauff in a star-studded second-round matchup after Gauff dominated Anhelina Kalinina 6-1 6-0.

She was simply too powerful for her Ukrainian opponent, winning 89 per cent (25-of-28) of her first serves to never give Kalinina a chance.

Canada's Bianca Andreescu was eliminated by American Shelby Rogers 6-4 6-2, while Russia's Veronika Kudermetova won a hard-fought battle against Italy's Camila Giorgi 7-6 (7-2) 4-6 7-5.

Meanwhile, in Washington at the Citi Open, Emma Raducanu looked in good touch as she handled the challenge of Louisa Chirico 6-4 6-2 to advance to the second round.

Raducanu will meet Colombia's Camila Osorio after she beat American Sofia Kenin 7-6 (7-2) 6-1, and top-20 talent Victoria Azarenka had no issues against Dayana Yastremska to win 6-4 6-0.

Australian Ajla Tomljanovic continued her strong run of form with a convincing 6-1 6-4 win against American Sloane Stephens, and the Czech Republic's Tereza Martincova recovered from a horrible first set to defeat Xinyu Wang 0-6 6-4 6-4.

Germany's Andrea Petkovic cruised to a 6-2 6-2 win against Denmark's Clara Tauson, and Russia's Anna Kalinskaya defeated American Madison Brengle 6-3 6-0.

Four-time major winner Naomi Osaka wants to simply get back to having fun upon her return to tennis at the Silicon Valley Classic this week.

The Japanese 24-year-old has not played since her first-round loss to Amanda Anisimova at the French Open in May and sits 41st in the world rankings. 

Osaka, who missed Wimbledon due to a left Achilles issue, parted ways with coach Wim Fissette last month after two and a half years.

The injury is one of many that have plagued Osaka over the past difficult 15 months, during which she withdrew from last year's French Open citing "mental health reasons" after boycotting her mandatory post-match media conferences.

She also announced a hiatus following her third-round US Open exit last year but appears in a better place now, with her father, Leonard Francois, stepping in as her coach.

"I just would like to have fun and I know I say that very often, basically every tournament for the last year now, but to genuinely have fun," Osaka told reporters.

"I was telling my dad literally this morning when we were practicing in the rain, years ago we would have to fight to practice on public courts. It was just me and my sister and my dad alone.

"Now I've gotten to the point where people pay to watch me play, and for that I am very grateful. I would have never imagined that as a child.

"Just having fun and being grateful in the moment and trying to engage with everyone to the best of my abilities."

Osaka moved to clarify there was nothing sinister behind her split with Fissette, having won the 2020 US Open and 2021 Australian Open titles alongside him.

"It was really good times with Wim and he's a really amazing coach," Osaka said.

"We didn't part on bad terms. I just felt I needed different energy, and at the same time, he's a very ambitious guy. I was getting injured and I'm sure he would have wanted to go to Wimbledon.

"It was two different mindsets, I would say. But he's a really cool guy still. So confirming that there were no bad things happening."

Osaka is due to face Qinwen Zheng in the first round at the Silicon Valley Classic on Tuesday.

Four-time grand slam champion Naomi Osaka will play her first tournament since the French Open at the Silicon Valley Classic after accepting wild card. 

The 24 has won a grand slam in each of the past four years, but crashed out in the first round at Roland Garros with a defeat to Amanda Anisimova – who also knocked her out of the third round of the Australian Open – before withdrawing from Wimbledon due to an injury concern.

Ir was announced on Monday that Osaka will make her return in hard-court event in San Jose that starts on August 1 - four weeks before the US Open gets under way.

Silicon Valley Classic tournament director Vickie Gunnarsson said it was a great outcome to add Osaka to the playing field in the competition where it all began for her.

"We are very excited to have Naomi Osaka returning to the Bay Area," she said. "She made her WTA debut at our event and watching her grow both on and off the court has been amazing.

"She is not only an incredible player but her commitment to equality and social change is truly inspiring."

Osaka is down in 38th place in the rankings and has not won a tournament this year, but reached the final of the Miami Open in April, losing to world number one Iga Swiatek.

Already confirmed for the Silicon Valley Classic are Wimbledon champion Elena Rybakina, world number five Ons Jabeur, young American star Coco Gauff and 2019 US Open champion Bianca Andreescu.

Rafael Nadal is halfway to a calendar Grand Slam, a feat that would mark the crowning point of any player's career.

Yet the Spanish great does not have to look far back into history to see how quickly that dream can be scuppered, with Novak Djokovic having fallen agonisingly short of a sweep of all four majors only last year.

As perhaps the most grounded player in tennis, Nadal heads into Wimbledon well aware that winning the first two majors of the year is no guarantee of any future success.

At the age of 36, and with a foot problem that requires careful maintenance, it would be arguably the most remarkable feat in the Open Era if Nadal were to add the Wimbledon and US Open titles to his Australian Open and French Open triumphs.

Such dominance is scarce in tennis, and Rod Laver was the last player to scoop all four men's singles titles at the majors, 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 Williams famously came unstuck when she faced Roberta Vinci in the semi-finals, while Djokovic went even closer in 2021, losing to Daniil Medvedev in the final at Flushing Meadows.

Here, Stats Perform examines the daunting challenge of scooping all four slams consecutively.

WHAT THE GREAT CHAMPIONS SAY

Before tennis reached its Open Era, which marked the dawning of professionalism on the tour, Laver won his first calendar Grand Slam in 1962.

He said later, quoted by the Tennis Hall of Fame: "It was a thrill to come off the court knowing I had won all four majors in one year. But I never felt like I was the best, never felt that way. I just happened to have a good year."

His 1969 dominance came a year after Laver returned to the majors, following a five-year exile while he played professional tennis elsewhere. When the majors allowed professionals to compete alongside the amateurs, 'Rocket Rod' was again unstoppable.

Laver turned 31 in 1969 and did not win any further grand slam singles titles in his career after that astonishing season, but that second perfect season sealed his legacy as an all-time great.

Stefan Edberg won a boys' singles clean sweep in 1983, but Laver remains the only player to win the men's singles full set in a calendar year since American Don Budge captured all four in the 1938 season, the first time it was achieved by a man. Maureen Connolly and Margaret Court achieved calendar Grand Slams in women's singles in 1953 and 1970 respectively.

A non-calendar Grand Slam was accomplished by Djokovic, when he won Wimbledon, the US Open, Australian Open and French Open consecutively across the 2015 and 2016 seasons. Yet no man other than Laver, Budge and Djokovic has won all four singles crowns in succession.

It has been 11 years since Nadal himself went close. He went to the Australian Open in 2011 with the Roland Garros, Wimbledon and US Open trophies in the bag, looking to complete the set.

"I am sure it's going to be the only one opportunity that I'm going to have in my life," said Nadal that year. "I'm not going to have more of these opportunities to win all four in a row.

"I think it is almost impossible. It is very, very difficult, no? Tennis is a very competitive sport and there is not a lot of difference between players. So a lot of matches are decided in a few balls. So for that reason it is very difficult to have one player winning everything. That's the truth."

Nadal, hampered by injury, lost in the Melbourne quarter-finals to David Ferrer in 2011 and had not won back-to-back slams since, until this year's surprise double. 

REACHING PRESSURE POINT

It is too soon to think that Nadal has a glorious chance to land all four big ones this year. After all, although he has won Wimbledon twice before, those triumphs came in 2008 and 2010, and he has a chronic foot problem. He has required radiofrequency ablation treatment in the past fortnight, preventing nerves in his foot sending messages to his brain.

He fell to Djokovic in the 2011 Wimbledon final and has not been back to the title match since, suffering a run of disappointing early exits in London before reaching semi-finals in 2018 and 2019, his last visits to the tournament.

Djokovic is a heavy favourite for this year's title, but it would be bold to entirely rule out Nadal, particularly given that as the second seed he cannot run into Djokovic until the final. Particularly given that he is Rafael Nadal, and prone to doing stupendous things.

Serbian Djokovic, a year Nadal's junior, would be able to tell his great rival just how intense the strain can become when a calendar Grand Slam becomes a serious prospect.

Speaking in November last year, two months after Medvedev denied him in New York, Djokovic said: "I'm very relieved that the grand slam season was done, because I felt a tremendous pressure unlike anything I felt in my life.

"It was an interesting experience, and I'm very satisfied with the way I played in grand slams, three wins and a final. There are much more positive things to be grateful for and to look at than negative."

Like Djokovic, Serena Williams has managed the non-calendar Grand Slam before, with the American first achieving 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 when she arrived at the US Open, having begun her dominant streak at her home grand slam the previous year.

That would have meant Williams sealed each of the 2015 slams, and losing to Vinci led to stark frustration, underlined by a 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," Williams said. "If you have any other questions, I'm open for that."

Sometimes, players get ahead of themselves when looking at the season ahead, and Naomi Osaka had a calendar Grand Slam in her thoughts after winning the season-opening Australian Open in 2019.

She had also triumphed at the US Open at the end of 2018, and the Japanese star was beginning to think she might enjoy an invincible year at the majors, only to stumble to a third-round French Open defeat to Katerina Siniakova.

Osaka said: "I think I was overthinking this calendar slam. For me this is something that I have wanted to do forever, but I have to think about it like if it was that easy, everyone would have done it."

Nick Kyrgios has become the first star to sign up to Naomi Osaka's sports agency. 

Australian Kyrgios was described by four-time grand slam winner Osaka as possessing an "unmatched style", while her business partner Stuart Duguid said the controversial ATP Tour player was "absolutely the icon" for young tennis fans. 

Osaka and Duguid, her long-time agent, announced the Evolve agency in May as both left IMG. 

Kyrgios, the extravagantly gifted world number 45, has won six career titles on the ATP Tour and has a world ranking high of number 13, with many considering him an unfulfilled talent. 

The 27-year-old won the Australian Open doubles title alongside countryman Thanasi Kokkinakis in January, and in singles he has reached consecutive semi-finals in his past three tournaments in Houston, Stuttgart and Halle. 

Osaka told Boardroom.TV that Kyrgios "embodies the types of athletes we want to work with". 

"He's got an unmatched style, passion and personality that is unlike any other in the sport," Osaka added. 

Duguid said: "Nick is the most talented and entertaining tennis player on the tour, bar none. His energy is infectious. And love or hate him, you definitely can't keep your eyes off him. For Gen Z and younger, he is absolutely the icon." 

While Kyrgios is planning to play at Wimbledon next week, Osaka will be absent, with the former world number one troubled by an Achilles injury.