Australian Open champion Novak Djokovic does not know if he will defend his crown due to the COVID-19 mandate in Victoria.

It remains to be seen whether world number one Djokovic will fly to Melbourne in January amid vaccination requirements.

The state of Victoria, where the year's opening grand slam takes place at Melbourne Park, has introduced a vaccine mandate for professional athletes and across most industries due to the coronavirus pandemic.

As doubts over Djokovic's participation linger, the 34-year-old superstar was asked about his Australian Open plans after losing to Alexander Zverev in the semi-finals of the ATP Finals on Saturday.

"I haven't been talking to [Tennis Australia], to be honest," nine-time Australian Open champion Djokovic told reporters after his 7-6 (7-4) 4-6 6-3 defeat in Turin.

"I was just waiting to hear what the news was going to be. Now that I know, we'll just have to wait and see."

The 2021 Australian Open went ahead, albeit in February instead of January, and without fans for most of the tournament following a snap lockdown of Melbourne due to COVID-19.

Djokovic – winner of a joint-record 20 grand slam titles – was among the players critical of the conditions athletes endured prior to this year's Australian Open, with strict quarantine measures introduced.