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.