Australia has detained Novak Djokovic for a second time, calling the World No 1 a threat to public order and fighting in court to deport him.
Having once failed to remove the unvaccinated 34-year-old from the country, Australia's government is trying again, but the Serb is challenging the ruling.
A federal court hearing is scheduled for Sunday and on Saturday Djokovic was placed under guard at an undisclosed Melbourne location, believed to be his lawyers' offices.
He will spend Saturday night in immigration detention, after a few days of freedom following his first successful court appeal.
In court filings, Australia has cast him as a catalyst for potential "civil unrest" who must be removed.
Djokovic's presence in Australia "may foster anti-vaccination sentiment", immigration minister Alex Hawke argued, justifying his use of executive powers to revoke his visa.
Not only could Djokovic encourage people to flout health rules, Hawke said, but his presence could lead to "civil unrest".
So just two days before the Australian Open begins, the defending champion is again focused on law courts rather than centre court.
Many Australians believe Djokovic used the system to dodge vaccine entry requirements.
After months of speculation about whether Djokovic would get vaccinated to play in Australia, he used a medical exemption to enter the country a week ago, hoping to challenge for a record 21st Grand Slam title at the Open.
Amid public outcry, Prime Minister Scott Morrison's government revoked Djokovic's visa on arrival.
But the government was humiliated when a judge reinstated Djokovic's visa and allowed him to remain in the country.
This time, the government has invoked exceptional - and difficult to challenge - executive powers to declare him a threat to public health and safety.
Djokovic's lawyers argue the government "cited no evidence" to support their claims.
The minister admitted that Djokovic is at "negligible" risk of infecting Australians, but argued his past "disregard" for Covid-19 regulations may pose a risk to public health and encourage people to ignore pandemic rules.
The Serb contracted Covid-19 in mid-December and, according to his own account, failed to isolate despite knowing he was positive.
Public records show he attended a stamp unveiling, youth tennis event and granted a media interview around the time he got tested and his latest infection was confirmed.
Djokovic is the Australian Open's top seed and a nine-time winner of the tournament. He had been practising just hours before Hawke's decision was announced.
The visa cancellation effectively means Djokovic would be barred from obtaining a new Australian visa for three years, except under exceptional circumstances, ruling him out of one of the four Grand Slam tournaments during that time.
Serbian President Aleksandar Vucic on Friday accused Australia of "mistreating" the country's biggest star, and a national hero.
"If you wanted to ban Novak Djokovic from winning the 10th trophy in Melbourne why didn't you return him immediately, why didn't you tell him 'it is impossible to obtain a visa'?" Vucic said on Instagram.
"Novak, we stand by you!"
Spanish great Nadal took a swipe at his rival on Saturday as players complained the scandal was overshadowing the opening Grand Slam of the year.
"The Australian Open is much more important than any player," Nadal said at Melbourne Park.
"Australian Open will be a great Australian Open with or without him.
"Honestly I'm little bit tired of the situation because I just believe that it's important to talk about our sport, about tennis."
Defending Australian Open champion Naomi Osaka called the Djokovic saga "unfortunate" and "sad" and said it could be the defining moment of his career.
"I think it's an unfortunate situation. He's such a great player and it's kind of sad that some people might remember (him) in this way," she said.
World No 4 Stefanos Tsitsipas criticised the 20-time Grand Slam winner and rival earlier this week, saying he was "playing by his own rules".