Victorian Premier Daniel Andrews says he's confident the 2021 Australian Open will proceed - but it remains to be seen how many international stars will compete as confusion reigns over quarantine requirements.
Andrews on Monday cast fresh doubt over the Open going ahead as scheduled from January 18-31 amid reports overseas players would not be allowed into Victoria in December.
Tennis Australia has been sweating for months on the Victorian and Australian governments allowing players to quarantine in a special training hub with their restricted entourages in Melbourne from mid-December.
That would allow the traditional lead-up events, including the multi-city ATP Cup, to be shifted from Sydney, Brisbane, Perth and Adelaide to Melbourne while some state borders remain closed.
Open tournament director Craig Tiley has categorically ruled out the Open being staged if players were forced into two weeks of hard quarantine before the season-opening grand slam.
Premier Andrews' claim on Monday that the Open proceeding was "not a done deal" prompted the ATP to issue a concerning memo to its representatives including superstars Roger Federer, Rafael Nadal and defending champion Novak Djokovic.
"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," the men's governing body said.
"We continue to work with Tennis Australia on confirming plans for January, and we will provide an update as soon as more information is available in the coming days.
"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 to players."
TA is understood to be frustrated by the Victorian government's approach, especially after Prime Minister Scott Morrison on Monday endorsed the Open going ahead as planned in its existing time slot.
Premier Andrews on Wednesday said negotiations and planning were "incredibly complex".
"It has to be done safely, it has to be done properly," he told reporters.
"We are working very, very closely with Tennis Australia. They are working (with) all of their partners and we're confident that we'll finish up with an Australian Open."
But if players are unable to start their quarantine period until January, that would mean no lead-in events being held before the gruelling fortnight-long Open - unless the biggest event on the annual Australian sporting calendar was pushed back into February.
That would complicate logistics, with hundreds of ballkids being back at school, although the second week of this year's Open was held after school had re-commenced in Victoria and it went ahead seemingly without a hitch.