SYDNEY, Jan. 15 (Xinhua) -- Athletes and their teams began arriving in Melbourne from Thursday ahead of next month's Australian Open (AO), despite several big names testing positive for COVID-19.

Former World No. 1 Andy Murray was unable to board one of the designated charter flights to Australia after testing positive for the virus, casting serious doubt on whether he will appear at the tournament.

After receiving the positive result, AO officials revealed that the three-time grand slam champion and five-time AO finalist was isolating at his home near London.

"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," AO officials said in a statement.

Shortly after, U.S. star Madison Keys revealed she too had tested positive for COVID-19 prior to boarding her flight to Melbourne and was self-isolating at home.

"I unfortunately tested positive for (COVID-19) before I was supposed to fly to Australia," Keys wrote on social media.

"I'm very disappointed to not be able to play in the coming weeks after training hard in the off-season and knowing Tennis Australia and the tours did so much to make these events happen."

Meanwhile, fellow-American Tennys Sandgren was granted special approval to travel to Australia for the event despite returning a positive result, having already been diagnosed and recovering from the disease last November.

Under the current rules, players are only allowed to enter Australia after returning a negative COVID-19 test taken just prior to departure, or with specific approval to travel as a recovered case.

"Tennys Sandgren's positive result was reviewed by health experts and determined to be viral shedding from a previous infection, so was given the all-clear to fly," Victoria's Minister for Police and Emergency Services, Lisa Neville said.

"No one who is COVID positive for the first time - or could still be infectious - will be allowed in for the AO."

Upon arrival, players and their teams are subject to the same two weeks of mandatory quarantine as other international arrivals, however players are allowed to undertake five hours of training per day at designated facilities which form part of a "quarantine bubble".