The Australian Open was plunged into a crisis on Saturday as positive COVID-19 cases were detected on two charter flights into Melbourne, forcing 47 players into hard lockdown for a fortnight.

Tournament officials said two passengers on a flight from Los Angeles that arrived on Friday morning had tested positive, along with one passenger who travelled in from Abu Dhabi.

None of those who tested positive were said to be players, although one was described as a "participant", which may mean a member of a player's entourage.

About 1,200 players and staff are arriving in Melbourne ahead of the delayed Australian Open, which is due to get under way on February 8.

They are travelling on sparsely populated aeroplanes to allow for social distancing, with 79 people, including 24 players, aboard the flight from Los Angeles and 64 people, including 23 players, arriving from Abu Dhabi. It was reported that players affected included recent grand slam champions.

A statement from the Australian Open said the players "will not be able to leave their hotel room for 14 days and until they are medically cleared. They will not be eligible to practise."

Australia's Department of Health and Human Services (DHHS) said those aboard the flights were considered 'close contacts' of those with the virus, and that means they will be confined to their hotel bedrooms for the next two weeks.

The Australian Open has pulled out all the stops in an effort to get the grand slam on, and that has meant all players have had to arrive early and go into quarantine, although most will be allowed to spend five hours outside their hotel rooms each day, to allow for practice and gym work.

Such limited liberties will not be afforded to those hit by the news of the positive tests on their flights.

French player Alize Cornet questioned why such steps were necessary, writing on Twitter: "Soon, half of the players from the AO will actually have to isolate. 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."

The 30-year-old world number 53 added: "I just think that these measures are not made to hold an international tennis event."

Cornet, who said she was not on an affected flight, believed there were meant to be measures in place to avoid wholesale lockdown in the case of positive tests.

She said: "We've been told that the plane would be separated by section of 10 people and that if one person of your section was positive, then you had to isolate. Not that the whole plane had to."

Victoria on Saturday recorded its 10th consecutive day with no locally acquired cases of coronavirus.

Madison Keys is set to miss the Australian Open after testing positive for coronavirus.

The 2017 US Open runner-up announced on Thursday that she contracted COVID-19 before she was due to fly out for the first grand slam of the year.

Keys did not state she will definitely miss the major, which starts on February 8, but it appears the American will not make the trip to Melbourne.

The American wrote on Instagram: "Hi everyone, I wanted to let you know that I unfortunately tested positive for COVID-19 before I was supposed to fly to Australia.

"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.

"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."

It was revealed earlier in the day that three-time major winner Andy Murray has also tested positive for the virus, but still hopes to play in the Australian Open.

Meanwhile, world number 50 Tennys Sandgren was cleared to board a flight from the United States bound for Melbourne despite revealing he returned a new positive coronavirus test this week. 

The American, twice a quarter-finalist at Melbourne Park, initially posted to social media on Wednesday that he had tested positive for the virus for a second time. 

Although his first instance of having the illness was recorded in November, the 29-year-old's participation in the tournament appeared to be in doubt. 

But as he continued to update followers through the day, it emerged he had been allowed to board his flight. 

Players will only be allowed into Australia with proof of a negative test just prior to departure, or with approval to travel as a recovered case at the complete discretion of an Australian government authority.

Anyone wanting to travel out for the tournament who previously tested positive is required to provide additional and highly detailed medical information as proof they are a recovered case and no longer infectious or a risk to the community.

The Australian Open has hinted Andy Murray will not be able to compete in Melbourne following his positive test for coronavirus.

Murray, a five-time finalist at the Australian Open, remains in good health and is isolating at home.

The three-time grand slam winner is still hoping to play and travel to Australia later than planned.

However, a statement from the tournament cast serious doubt on his involvement, with Murray – ranked 123rd in the world – having initially been granted a wildcard to play.

The statement read: "Andy Murray has advised that he has tested positive for COVID-19 and is isolating at home in the UK.

"Unfortunately, this means that 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."

The first grand slam of the year is starting three weeks later than it normally would on February 8 due to the complications of players flying into Australia amid the ongoing coronavirus pandemic.

Tournament organisers are putting on 15 chartered flights, which will operate at 25 per cent capacity, to bring players to the tournament.

Before boarding, competitors must test negative and will undergo a series of tests once in the country, while undergoing a 14-day quarantine period in Melbourne.

It was after a first-round defeat at the Australian Open two years ago that Murray stated his career might be over due to an ongoing hip injury.

Andy Murray's participation at the Australian Open is in doubt following a positive COVID-19 test.

Three-time grand slam champion Murray remains in good health but is isolating at home.

The 33-year-old Briton is still hopeful of being able to travel to Australia later than planned and taking part in the first grand slam of the year.

Murray received a wildcard for the Australian Open, where he has been a runner-up on five occasions.

It is set to be the Briton's first participation at Melbourne Park since announcing after a first-round loss in 2019 that his career was in the balance due to a persistent hip injury.

The Australian Open is scheduled to get under way on February 8.

Rafael Nadal will be without his coach Carlos Moya due to the pandemic, while Dominic Thiem's coach Nicolas Massu tested positive before travelling to Australia.

It is still hoped that Massu can make the trip following a negative result.

Tennys Sandgren was cleared to board a flight from the United States bound for Melbourne ahead of the Australian Open despite revealing he returned a new positive coronavirus test this week. 

The American, twice a quarter-finalist at Melbourne Park, initially posted to social media on Wednesday that he had tested positive for the virus for a second time. 

Although his first instance of having the illness was recorded in November, the 29-year-old's participation in the tournament appeared to be in doubt. 

But, as he continued to update followers through the day, it emerged he had been allowed to board his flight. 

Writing on Twitter, he said: "Wait hold on I think they are trying to get me on 15 min [sic] after the plane was supposed to depart.. my bags still aren't checked lol." 

A follow-up read: "Wow I'm on the plane. Maybe I just held my breath too long. Craig Tiley [Tennis Australia] is a wizard." 

Some expressed concerns about the possibility of Sandgren potentially spreading the virus to fellow passengers and then locals once he arrives in Australia. 

But a statement from the Australian Open has looked to reassure people that players' infectiousness is checked prior to boarding flights. 

It 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.

"Any recovered case must go through this process in order to have an opportunity to travel here for the Australian Open. No one can travel without either proof of a negative test or this special clearance from authorities confirming they are not infectious. 

"Upon arrival all players are immediately placed in a secure quarantine environment for 14 days under the authority of COVID Quarantine Victoria, and will undergo a more rigorous testing schedule than most returning travellers." 

An earlier statement issued by the tournament organisers in reply to Sandgren's tweets said: "Some people who have recovered from COVID-19 and who are non-infectious can continue to shed the virus for several months. 

"Victorian Government public health experts assess each case based on additional detailed medical records to ensure they are not infectious before checking in to the charter flights. 

"Players and their teams are tested every day from their arrival in Australia, a much stricter process than for anyone else in hotel quarantine." 

The first grand slam of the year is due to begin on February 8 after being delayed due to the pandemic. 

Initially it was to run from January 18-31 but was pushed back to help give qualifiers time to travel and complete a two-week quarantine in Australia prior to warm-up events getting under way at the end of the month. 

Players at Melbourne Park will have to follow strict guidelines and protocols, including a five-hour limit on training with a maximum of one team member. 

The teams must stay in their hotel for the other 19 hours of every day, and players have to return six negative COVID-19 tests before being allowed to play.

Roger Federer decided to miss the Australian Open because wife Mirka opposed having to spend a full fortnight in quarantine, a leading official has claimed.

It was widely assumed Federer's reason for skipping the upcoming grand slam related to the knee surgery he underwent last season.

He had hinted as much, and agent Tony Godsick referred to the knee rehabilitation when announcing in December that the Swiss great would not travel to Melbourne.

But Andre Sa, the head of player liaison at Tennis Australia, says Federer pulled out when it became apparent his wife and children would be holed up in their hotel accommodation for two weeks.

The players travelling to Australia must all quarantine to avoid any possible spread of COVID-19, but they are allocated five hours per day in which they can leave their rooms to train and practise with specified hitting partners.

Sa, a former top-20 doubles player, told Band Sports in his native Brazil that he discussed with father-of-four Federer the practicalities before the 20-time grand slam winner reached his decision.

"The main reason was the quarantine," said Sa. "I talked to him a month ago and he had two options. He could come with the whole family and do the quarantine.

"The problem is that Mirka and her children couldn't leave the room. They would have to stay 14 days in the room. The exception is only for players.

"He could go out, train and come back, but the family couldn't. Mirka did not approve the idea.

"The other option would be for him to come alone. Only there would be at least five weeks away from family and children. And then he said, 'Dude, 39, four kids, 20 grand slams. I'm no longer at the stage to be away from my family for five weeks.'"

Former world number one Federer has not played a tournament since losing to Novak Djokovic in the semi-finals of the Australian Open last year.

This year's edition of the grand slam has been delayed by three weeks to a February 8 start, due to factors tied into the pandemic.