Top-ranked tennis player Novak Djokovic said he's "opposed to vaccination" and doesn't like the idea of being required to get a coronavirus vaccine in order to return to playing, once a vaccine is developed. He made the controversial remarks in a Facebook chat with other Serbian athletes Sunday.

"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, according to a translation from Reuters. "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."

Public health officials say it's likely to take at least a year to 18 months before a vaccine could become available. The World Health Organization said in a report last last week that three potential vaccines are currently being tested in clinical trials and 67 others are in earlier stages of evaluation.

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In March, retired tennis star Amelie Mauresmo tweeted that there should be no return to pro tournaments until there's a vaccine.

"International circuit = players of all nationalities plus the staff, spectators and people from the 4 corners of the world who bring these events to life," she wrote. "No vaccine = no tennis."

Much like the rest of the sports world, tennis has faced cancellations of its events amid the pandemic. Wimbledon was canceled for the first time since 1945 — in the middle of World War II. The French Open, originally slated to start in mid-May, was rescheduled for the fall.