Forty-seven players competing in the Australian Open, including Britain's Heather Watson, will be forced to remain in their hotel rooms for 14 days following three positive Covid-19 tests.
Two people on a chartered flight from Los Angeles carrying 24 players returned positive swabs upon their arrival in Melbourne.
On a later flight from Abu Dhabi, a sole passenger on a plane carrying 23 players also returned a positive result.
Victoria’s Department of Health and Human Services said that the infected trio were not players.
The world’s top players began arriving in the country on a series of charter jets on Thursday ahead of a two-week quarantine period, during which they will be allowed out of their rooms to practice for five hours a day.
But those players and support staff on the affected flights will now be confined to their rooms for a fortnight.
British number two Watson arrived from Abu Dhabi.
The 28-year-old tweeted: “One person on the flight I was on from Abu Dhabi tested positive. So now everyone else who was on that flight has a 14-day quarantine where we are NOT allowed out our rooms.
“The same happened on one of the chartered flights from Los Angeles. 2 flights... so far.”
Sylvain Bruneau, coach to former US Open champion Bianca Andreescu, subsequently revealed that it was he who had tested positive, with Canadian Andreescu among those now isolating along with big names such as Victoria Azarenka, Angelique Kerber and Kei Nishikori.
The Australian Open begins on February 8th, meaning those players on the affected flights will be restricted to little more than a week of practice.
Following the first affected flight, Australian Open tournament director Craig Tiley said in a statement: "We are communicating with everyone on this flight, and particularly the playing group whose conditions have now changed, to ensure their needs are being catered to as much as possible, and that they are fully appraised of the situation.
“Our thoughts are with the two people who tested positive on the flight and we wish them well for their recovery.”
Reports then emerged of a positive test among the cohort of top players and their practice partners who are quarantining separately in Adelaide.
Serbian media reported that the fitness trainer of Filip Krajinovic, Novak Djokovic's practice partner, had tested positive but it would not result in contacts having to isolate because he had recently overcome the virus and was not infectious.
A similar reason was given for American player Tennys Sandgren being allowed to travel despite a positive test on Monday.
A message on the Australian Open’s Twitter feed read: “Update from Adelaide: SA Health has confirmed that there is no one who has an active COVID-19 infection in the entire tennis cohort based in Adelaide. Testing will continue on a daily basis.”
There have already been gripes from other players about perceived preferential treatment given to the group in Adelaide, which also includes Rafael Nadal, Serena Williams and Naomi Osaka.
Tournament organisers spent several months negotiating an arrangement regarding the admission of more than 1,000 tennis players and associated personnel to Australia.
It was widely accepted that a quarantine restricting players to their rooms for two weeks would not be acceptable and several players took to social media to voice their concerns.
One complaint was that they had been told planes would be separated into sections to reduce the danger of a whole plane-load having to isolate should anyone test positive.
The fact the Australian Open has been allowed to go ahead has been hugely controversial given Victoria’s ultra-strict approach to tackling coronavirus and while thousands of Australians remain stranded overseas because of a limit on numbers allowed into the country.
News of positive tests will stoke the fires further, while it is unlikely to help the cause of Andy Murray, who is hoping to negotiate entry at a later date after contracting coronavirus and missing the charter flight while he isolates at home in Surrey.
