Forty-seven players were barred from practising for a fortnight Saturday in a major setback to their Australian Open preparations after passengers on two charter flights that brought them to Melbourne tested positive for Covid-19.
One of the positive tests was returned by Sylvain Bruneau, the coach of Canada's 2019 US Open winner Bianca Andreescu.
He said he was "saddened and sorry for the consequences" after arriving on a flight from Abu Dhabi.
Everyone on board the two flights, considered as close contacts, has been ordered to stay in their hotel rooms for the entire 14-day mandatory quarantine period.
That included 24 players on a plane from Los Angeles, where a crew member and one other passenger, reportedly a coach, tested positive.
According to local media, former Australian Open champion Victoria Azarenka, 2017 US Open winner Sloane Stephens and Japan's Kei Nishikori were among those on board.
Twenty-three players, including Grand Slam winners Andreescu, Angelique Kerber and Svetlana Kuznetsova were on the flight from Abu Dhabi.
Bruneau said that he had tested negative within 72 hours of his flight's departure from the Gulf and "felt perfectly fine when I boarded."
He insisted he had followed all the protocols while in the Middle East.
"I have no idea how I might have contracted this virus."
He added: "The rest of my team is negative and I sincerely hope that any further disruption is kept to a minimum."
'Hard work going to waste'
French player Alize Cornet, who is in Melbourne but was not on either plane, called the situation "insane".
"Soon, half of the players from the AO will actually have to isolate," she tweeted.
"Weeks and weeks of practice and hard work going to waste for one person positive to Covid in a 3/4 empty plane. Sorry but this is insane."
Other players claimed that the rules governing confinement have been changed.
"We are not complaining to be in quarantine," tweeted Swiss world number 12 Belinda Bencic.
"We are complaining because of unequal practice/playing conditions before quite important tournaments."
Romania's Sorana Cirstea, ranked 71, tweeted: "I was planning to play the tournament because they promised daily 5 h quarantine exemption where we could go practice, do a gym session and rehab. This was the deal before signing up to this...but the rules changed 'overnight'!"
The world's top players began arriving in Australia on Thursday for the delayed Grand Slam, which is due to start on February 8.
All must undergo a 14-day quarantine, but are allowed out for five hours daily to train in strict bio-secure bubbles ahead of a host of warm-up tournaments, all in Melbourne, in the week leading up to the Grand Slam.
According to the Melbourne Herald Sun, the Los Angeles flight was the same one that sparked controversy on Thursday when American player Tennys Sandgren tweeted he had been allowed to board despite returning a positive test.
It was his second positive result, having been diagnosed with Covid-19 in November, but Victorian state health chiefs insisted his infection was historical and he had "met the rigorous health criteria that has been set".
Players were only allowed to board with proof of a negative test prior to departure, or with approval as a recovered case at the discretion of the Australian government, as with Sandgren.
It was the latest setback for a tournament that has spent months working through the logistical nightmares of hosting a Grand Slam during a pandemic, with Melbourne only emerging from months of lockdown in October.
The tournament has already lost some key players, with Roger Federer out injured and world number 25 John Isner opting not to travel due to the coronavirus restrictions.
Three-time major winner Andy Murray tested positive for the virus and is isolating at home in London, casting doubt on whether he will be able to play.
American world number 16 Madison Keys also tested positive, and pulled out.
Meanwhile, world number three Dominic Thiem arrived without coach Nicolas Massu, another to test positive, and Nadal is missing his coach Carlos Moya who has decided not to make the trip.