Tennis chiefs insisted American Tennys Sandgren was not a coronavirus risk after he sparked a flurry of concern by tweeting he'd boarded a flight for the Australian Open in Melbourne despite testing positive.

The world No.50 is among more than 1,200 players and support staff arriving in Australia from Thursday for 14 days' quarantine ahead of the delayed Grand Slam, which is due to start on February 8.

Sandgren sent out a series of tweets before his departure from Los Angeles, initially saying he tested positive on Monday and would miss his flight. It was his second positive result, having originally been diagnosed with COVID-19 in November.

But an hour later he said, "Wow I'm on the plane. Maybe I just held my breath too long. Craig Tiley is a wizard."

Tiley, the Australian Open tournament director, has spent months trying to deal with the logistical nightmares of hosting the Grand Slam during a pandemic.

Tennis Australia said players were only allowed into Australia with proof of a negative COVID-19 test prior to departure, or with approval as a recovered case at the discretion of the Australian government.

"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," it said. 

"Upon completion of that review he was cleared to fly."

But in a country that largely has the coronavirus under control, it caused jitters on social media where Sandgren was a top trending topic. Melbourne only emerged from months of lockdown in October.

"We're nervous enough about tennis players flying in & being irresponsible - please don't joke about this," tweeted one person.

Sandgren later tweeted to clarify. "My two tests were less than [eight] weeks [apart]. I was sick in November, totally healthy now. There's not a single documented case where I would be contagious at this point. Totally recovered!"