Novak Djokovic said he has not yet decided whether he would compete at January's Australian Open after organisers confirmed that all players must be vaccinated against COVID-19 if they want to compete at the season's opening Grand Slam event.
"We'll see. We'll have to wait and see," world number one Djokovic told reporter after his semi-final defeat by Alexander Zverev at the ATP Finals on Saturday.
Djokovic, who has declined to say publicly if he has been vaccinated, is currently tied with Roger Federer and Rafa Nadal with 20 Grand Slam titles.
The Australian Open, which he has won nine times, is seen as a golden opportunity for him to take the lead over his rivals.
Nadal confirmed he would play at Melbourne Park in January but Federer, who like the Spaniard is also fully vaccinated, will miss the tournament as he recovers from another knee surgery.
Australia Open chief Craig Tiley's announcement brought to a conclusion months of negotiations between Tennis Australia and the Victoria state government, which had insisted throughout that everybody at Melbourne Park would need to be vaccinated.
Zverev said players need to respect that decision.
"We are visiting another country. This is not about tennis," he said after defeating Djokovic to advance to Sunday's ATP Finals championship match.
"This is about the virus that is going on. We need to follow the rules and follow the guidelines. I hope he's able to play."