July 21 (Reuters) - Naomi Osaka will defend her title at the U.S. Open, organisers said on Wednesday, after she withdrew from this year"s French Open and Wimbledon on mental health grounds. Japan"s Osaka stunned the tennis world when she quit the claycourt major in Paris in May following her first-round match after being fined and threatened with disqualification when she refused to attend mandatory post-match press conferences. read more The world number two, who said she had social anxiety, also skipped Wimbledon but is scheduled to play at the Tokyo Olympics and then in Montreal next month. read more Osaka will be part of a women"s field at the U.S. Open that will also include world number one Ash Barty, who lifted her second major title at Wimbledon earlier this month. A total of 15 major winners, including Simona Halep and Garbine Muguruza, are scheduled to feature in the women"s field at Flushing Meadows. In the men"s section, former champions Novak Djokovic, Roger Federer and Rafael Nadal -- currently tied for the men"s record of 20 Grand Slam singles titles -- will resume their quest for more silverware in New York. World number one Djokovic, fresh from his third major triumph of 2020 at Wimbledon, is aiming to become the first man since Australia"s Rod Laver in 1969 to complete a calendar year sweep. Another former champion, Andy Murray, who is currently ranked 104, failed to make the main draw but remains the first player on the alternate list. The U.S. Open will be held with 100% fan capacity from Aug. 30 to Sept. 12.