Novak Djokovic said he faces a dilemma if it becomes compulsory for players to get vaccinated before they can return to competing, as he is opposed to vaccinations.
Much of the sporting calendar has been halted as the coronavirus pandemic continues to sweep the world.
"Personally, I am opposed to vaccination, and I wouldn't want to be forced by someone to take a vaccine in order to be able to travel," Djokovic said in a live Facebook chat on Sunday with several fellow Serbian athletes. "But if it becomes compulsory, what will happen? I will have to make a decision. I have my own thoughts about the matter, and whether those thoughts will change at some point, I don't know.
"Hypothetically, if the season was to resume in July, August or September, though unlikely, I understand that a vaccine will become a requirement straight after we are out of strict quarantine, and there is no vaccine yet."
In a statement to The Associated Press on Tuesday, Djokovic said many tennis players and other athletes have asked him for his opinion on this situation.
"I have expressed my views because I have the right to and I also feel responsible to highlight certain essential topics that are concerning the tennis world," he said.
Djokovic and his wife, Jelena, advocate natural healing and not vaccinations, and he said that like the rest of the world, he was "a bit confused."
"I am no expert, but I do want to have an option to choose what's best for my body," he said. "I am keeping an open mind, and I'll continue to research this topic because it is important and it will affect all of us."
Prominent Serbian epidemiologist Predrag Kon, a member of the state team fighting the spread of COVID-19, said Djokovic should not have made anti-vaccination statements because of his huge public influence in his native Balkan country.
Last month, former world No. 1 Amelie Mauresmo said the rest of the 2020 tennis season might be wiped out, saying that action should not resume before players can get vaccinated against the coronavirus.
"International circuit = players of all nationalities plus management, spectators and people from the 4 corners of the world who bring these events to life. No vaccine = no tennis," the two-time Grand Slam winner said in a widely shared tweet.
Medical experts have said that vaccines against the respiratory virus would not be ready until next year, raising doubts whether any further tennis tournaments can be played this year.
Wimbledon has been cancelled for the first time since World War II, while the French Open, originally due to be held from May 24-June 7, was rescheduled for Sept. 20-Oct. 4, shortly after the end of the US Open.
Djokovic made a flying start to the 2020 season, winning the Australian Open in January for his 17th Grand Slam title. He stretched his winning run to 18 matches before the pandemic brought the sports world to a halt.
The 2020 Tokyo Olympics and the Euro 2020 soccer championship were among the events postponed until next year, as the pandemic has caused 165,000 deaths worldwide.
So far, the governing bodies of tennis have suspended all tournaments until July 13. In addition, the women's Rogers Cup in Montreal, which had been due to be held in August, will also not take place this year.
Reuters and The Associated Press contributed to this report.