Australian Open boss Craig Tiley said Sunday there was still "quite a bit to play out" on whether Novak Djokovic will defend his title in Melbourne, with a clearer picture "in the coming days".
The 20-time Grand Slam champion has refused to confirm if he has been vaccinated against Covid-19 and withdrew from the ATP Cup in Sydney this week without giving a reason.
All participants at the opening Grand Slam of the year, which starts January 17, need to be vaccinated or have a medical exemption.
There is speculation that Djokovic has applied for one, which would be assessed by an independent panel of experts and remain confidential.
Tiley said the clock was ticking.
"We've still got a few charter flights coming in until the end of this week and then all the players will be here," he told the Nine Network.
"As far as the status relates to Novak, I think we'll have a much clearer picture in the coming days otherwise it's getting pretty late to show up and play the Australian Open."
"There's quite a bit to play out and I think it will play out in the coming days," he added.
Government officials in Victoria state, which hosts the Australian Open, have been adamant for months that only vaccinated players can play the tournament.
"They're the rules. Medical exemptions are just that -- it's not a loophole for privileged tennis players," the state's Deputy Premier James Merlino said in December.
Djokovic's arch-rival Rafael Nadal, who is also gunning for record 21st Grand Slam title, is already in Melbourne preparing after recovering from the coronavirus.
Fellow 20-time Grand Slam winner Roger Federer is sidelined by injury.