Novak Djokovic, the world’s No. 1 men’s tennis player, caused a stir with comments over the weekend suggesting he would have a difficult decision to make if receiving a coronavirus vaccine became mandatory to compete on the tennis circuit.

“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 comments reported and translated Sunday by 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.”

Djokovic, the 32-year-old Serbian star who has won 17 Grand Slam singles titles, was speaking with a group of Serbian players on a live Facebook chat when he made the comment. Djokovic is staying in Spain with his wife, Jelena, and their two children during the lockdown.

In a statement released Monday through his management team, Djokovic declined to address whether he opposed vaccines in general. He focused his opposition on the issue of whether a Covid-19 vaccination, which has not been developed yet, would be necessary for travel. He also made it clear that he was intent on exploring options other than vaccination, but he did not rule out accepting one if necessary.