London - Rafael Nadal faces a battle to qualify for the Rio Olympics after the International Tennis Federation announced the entry list Thursday for the 2016 Games.
The ITF published the list of players whose place in the Rio draw is assured -- though a question mark hangs over the name of 2008 Beijing champion Nadal.
The injured world number four planned to return to action at Toronto on July 25, but his place rests on him making himself available for Spain away to Romania in the Davis Cup on July 15 or a last-ditch appeal.
The 30-year-old is sitting out Wimbledon after failing to recover from the wrist injury which forced his early withdrawal from the French Open last month.
Nadal is keen to play in Rio after being unable to defend his gold medal at the London 2012 Games due to a knee injury.
The ITF Olympic Committee said it would discuss any outstanding men's appeals on July 15 regarding any player who still had the chance to compete in the July 15-17 Davis Cup ties.
Reigning champions Andy Murray and Serena Williams will defend their Olympic titles on the Rio hard courts, the ITF confirmed.
Top stars including world number one Novak Djokovic, Roger Federer, Stan Wawrinka and Kei Nishikori, Grigor Dimitrov and Milos Raonic have their places booked in the men's draw.
In the women's competition, Victoria Azarenka, Eugenie Bouchard, Petra Kvitova, Caroline Wozniacki, Agnieszka Radwanska, Garbine Muguruza, Ana Ivanovic and Venus Williams have their spots confirmed.
Denmark's Wozniacki was relieved by the announcement after winning an appeal.
"It's been a long wait but I am officially going to Rio! Rocking the Danish colours on court!", said Wozniacki who is due to carry her country's flag at the opening ceremony.
All four US men's players Jack Sock, Steve Johnson, Denis Kudla and Brian Baker have their places subject to participation in the July Davis Cup ties or an appeal to the ITF Olympic Committee.
Argentina's Juan Martin del Potro and Juan Monaco also have a question mark hanging over their participation.
There is a limit of four singles players per gender per country. Sixty-four players will compete in each draw.
Entries are subject to players being in good standing with their national association and meeting the minimum participation requirements in men's Davis Cup and women's Fed Cup.
Australia will be represented by John Millman and Thanasi Kokkinakis after the highly-temperamental Nick Kyrgios pulled out, blaming "unwarranted attacks" on him by Australian Olympic chiefs after he was warned to behave.
His decision followed compatriot Bernard Tomic making himself unavailable for selection last month after widespread criticism about his recent on-court attitude and behaviour.
"Since the return of tennis to the Olympics in 1988, the event has continued to grow at each Games, with the current generation of players embracing this unique opportunity in our sport," said ITF president David Haggerty.
"We expect that the competition in each discipline will be fierce, and look forward to some memorable matches."
The draw will be staged on August 4. The nine-day tournament begins on August 6.