Andy Murray's participation at the Australian Open is in doubt after he tested positive for coronavirus.
The former World No.1 was due to travel to Australia on one of the charter flights laid on by tournament organisers but is still isolating at home.
It is understood that Murray, who is said to be in good health, is hoping to be able to arrive in Australia at a later date and participate in the year's first Grand Slam, which begins on February 8 in Melbourne.
Murray and his team are working closely with tournament director Craig Tiley to try to come up with an acceptable solution.
Tournament organisers spent several months negotiating an arrangement that was acceptable to local and national government agencies regarding the admission of more than 1,000 tennis players and associated personnel to Australia.
A statement from the Australian Open did not appear to offer Murray too much hope, saying: "Andy Murray has advised that he has tested positive for Covid-19 and is isolating at home in the UK.
"Unfortunately this means he will be unable to join the official AO charter flights arriving in Australia in the coming days to go through the quarantine period with the other players.
"The AO fans love Andy, and we know how much he loves competing here in Melbourne and how hard he'd worked for this opportunity."
Players began arriving in the country yesterday ahead of a two-week period of quarantine, during which they are allowed out of their rooms to practice for five hours a day.
They were told that a positive test prior to flying would mean they were not allowed to travel to Australia.
Murray has been given a wildcard for the tournament and is hoping to make his first appearance in Melbourne since the emotional events of 2019, when he revealed the extent of his right hip problems and raised the possibility of imminent retirement.
A resurfacing operation shortly afterwards allowed him to resume his career that summer but he has experienced several setbacks since, the most recent an issue with his left psoas muscle, which connects the spine to the femur.
He spoke positively about his fitness in November and last month played two matches at the most recent Battle of the Brits event, beating Dan Evans and Cameron Norrie.
World No.16 Madison Keys will not be making the trip after testing positive, with the American saying on Twitter: "I am self-isolating at home and will continue to follow all the necessary health precautions. I look forward to being back on tour next month."
Meanwhile, tournament organisers have explained why American player Tennys Sandgren was allowed to travel to Australia despite testing positive for Covid-19 on Monday.
Sandgren, a two-time quarter-finalist in Melbourne, had coronavirus in November and is therefore no longer deemed infectious.
An Australian Open statement read: "In the case of Tennys Sandgren, who has self-disclosed that he previously tested positive in late November, his medical file had to be reviewed by Victorian health authorities. Upon completion of that review he was cleared to fly."
World No.2 Rafael Nadal and last year's Australian Open finalist Dominic Thiem have both suffered setbacks, with their coaches unable to make the trip Down Under.
Players and officials have to undergo a mandatory 14-day quarantine on arrival in Australia before they participate in warm-up events from January 31 at Melbourne Park, where the Major will be held from February 8-21.
Nadal's coach Carlos Moya said he would not be travelling due to the health restrictions.
"After speaking with Rafa, we have decided that I won't travel to Australia with the team," Moya, a former World No.1, said on social media. "I will follow the tournament from home and will stay with my family, parents and kids due to the delicate situation that Spain is living with the virus. Best of luck to the team."
Nadal, US Open champion Thiem, ranked No.3 in the world, and defending Australian Open winner Novak Djokovic will be among the top players quarantining in Adelaide before heading to Melbourne.