Tennis world No. 1 Novak Djokovic contracted COVID-19 last month but was not experiencing symptoms and had written clearance from Australia's immigration department before traveling to the country with a medical exemption from its vaccination rules, his lawyers said in a court filing on Saturday.

Djokovic, who is in immigration detention in Australia after having his visa canceled on arrival on Thursday, returned his first positive coronavirus test on Dec 16 but 14 days later "had not had a fever or respiratory symptoms of COVID-19 in the last 72 hours," the filing said, which is seeking to overturn the cancellation of his Australian entry visa.

On Jan 1, the Serbian sports star received  "a document from the Department of Home Affairs (which) told Mr. Djokovic that his 'responses indicate(d) that (he met) the requirements for a quarantine-free arrival into Australia," the documents added.

The 34-year-old has never disclosed his own vaccination status. He is challenging his visa cancellation in Australia's federal court in hopes of winning his 21st Grand Slam at the Australian Open, which starts on Jan 17.

"I explained that I had been recently infected with COVID in December 2021 and on this basis I was entitled to a medical exemption in accordance with Australian Government rules and guidance," Djokovic says in the filing about his experience being detained at Melbourne Airport. 

Djokovic says he told Australian Border Force "officers that I had correctly made my Australian Travel Declaration and otherwise satisfied all necessary requirements in order to lawfully enter Australia on my visa".

The federal court has ordered Home Affairs to file its response by Sunday.

On Friday, the Serb thanked people around the world for their support on Instagram, "Thank you to people around the world for your continuous support. I can feel it, and it is greatly appreciated."

Meanwhile, the detention has fueled anger and charges of racism in his native Serbia. Hundreds have rallied for the past two days in support of the tennis star, the president has evoked a "political witch hunt," and Serbia's religious leader has called for the nation to offer prayers for their favorite son.

"It's a shame what is going on," said Dusan Stojic, a 67-year-old pensioner, who shed tears during a demonstration in Belgrade.

"It's not the vaccine that's the problem, it's because he's Serbian and the best tennis player in the world," tweeted Djokovic fan Marinko Bulatovic.

"Enough of the chicanery and abuse just because the greatest comes from a small country in the Balkans," added Marija Santic.

On Saturday evening, Czech tennis player Renata Voracova, placed in the same Melbourne detention center, was seen by reporters leaving the hotel in a van.

Her destination was not immediately clear,

Unlike Djokovic,  she earlier revealed that she was planning to go back home, describing her stay felt like "being in prison". 

"I'm in a room and I can't go anywhere," the 38-year-old Voracova, ranked 81st in doubles, told the Czech dailies DNES and Sport.

"My window is shut tight, I can't open it 5cm.

"And there are guards everywhere, even under the window, which is quite funny. Maybe they thought I would jump and run away," added Voracova, "they bring me food and there's a guard in the corridor. You have to report, everything is rationed. I feel a bit like in prison."

Unvaccinated against COVID-19, Voracova was allowed to enter on an exemption after recovering from the disease late last year, and she even managed a doubles match at a Melbourne WTA event. 

"I don't understand why they would come to me after a week and say, look, the rules that applied do not apply anymore."

"... I'm waiting for a permit (to leave), on Saturday perhaps," said Voracova, who has won 11 WTA doubles titles during her career.

(With input from agencies)