Playing the Australian Open with no preparation time would be "very dangerous", Brazilian doubles specialist Bruno Soares warned on Wednesday, after lead-up events to the Grand Slam were thrown into further doubt.
The stark message came after Australian tennis chiefs flagged "new challenges" around the arrival of players during the coronavirus pandemic.
In correspondence with players, the ATP -- the men's tennis tour -- said arrivals originally planned for December were now uncertain, potentially disrupting the packed January schedule.
With players facing a 14-day quarantine, any delay could make it difficult to hold the high-profile ATP Cup and other tournaments before the scheduled start of the Australian Open in Melbourne on January 18.
"In discussions with Tennis Australia over the past 24 hours, we have been informed there are some new challenges around the previously planned arrival dates for players and team members," read the ATP's message, which was tweeted by world number 193 Lukas Lacko.
"We understand there is uncertainty about the start of the 2021 season, and we are working as hard as possible to deliver the best possible calendar of events," the ATP added.
International travel to Australia is still tightly controlled and all overseas arrivals must quarantine for two weeks, while individual states also have their own Covid-19 restrictions.
It is also unclear whether players will be allowed to train during quarantine.
Soares, playing in the doubles event at the ATP Finals in London this week, said it would be tough to play with no practice.
"If we have to quarantine for 14 days inside a room and then go play a Grand Slam, I mean, I will do it because it's my job and I have to find a way," said the Brazilian, a member of the ATP player council.
"But I think it's quite dangerous for the players with no preparation I think to go there and compete right away. I think it's physically very dangerous."
- Zverev fear -
Alexander Zverev, bidding to win a second ATP Finals singles title, said he was also concerned.
"If we can't even practise for 14 days and we have to go out to play the Australian Open, it's a lottery," he said. "I mean, you can basically flip a coin who wins."
Reigning Australian Open champion Novak Djokovic, also playing in London, said he understood there were several options on the table and he would be prepared for the tournament to be pushed back a week.
"I'm planning to play Australian Open for sure," he said. "I mean, I would like to go there and I'm ready to quarantine for two weeks and whatever is necessary for me to be able to play.
"I hope that there is going to be support and understanding from the Victorian and Australian government for the players and for Tennis Australia and that they will allow players to compete in the second week of quarantine."
Tennis Australia on Monday flagged plans to move warm-up events from across Australia to the state of Victoria, to mitigate against any possible state border closures.
But Victoria's state premier Dan Andrews said the move was "not a done deal", particularly since Melbourne only recently emerged from a month-long lockdown.
Australia has been relatively successful in containing the virus, with just over 27,700 cases and 907 deaths recorded since the pandemic began.
But an outbreak in South Australia, which neighbours Victoria, triggered a six-day lockdown Wednesday as officials rush to contain a cluster in Adelaide.