Novak Djokovic probably "did not know" of his own positive Covid-19 test result when he mixed with the public in Serbia without a mask, his mother said Wednesday in a television interview.

The unvaccinated tennis superstar was seen in Belgrade after he claims he tested positive for Covid-19 on December 16 -- the basis for the vaccine exemption he used to enter Australia.

On December 17, the day after the positive PCR test result, he attended the launch of a Serbian stamp bearing his image and he also appeared unmasked beside young tennis players in Belgrade.

"He did not know probably," his mother Dijana told Australia's Channel 7 television.

"He did not know because when he realised that he is positive then he go to isolation because he did not know," she said, suggesting that it would be better to ask Djokovic himself.

Serbian Prime Minister Ana Brnabic said it would be a "clear breach" of the country's Covid-19 rules if the tennis world number one was in public while knowing he had tested positive.

"If you're positive you have to be in isolation," Brnabic said in an interview with the BBC.

It was unclear when the player knew of his result, she said.

"I do not know when he actually got the results, when he saw the results, so there is some grey area," she told the broadcaster.

"The only answer to this can be provided by Novak."

Questions have also been raised in Australia over a single answer given on the 34-year-old's travel declaration, which must be submitted before starting the trip.

His travel document, which has been released by the federal circuit court, has a tick on the box to show that he had not and did not plan to travel in the 14 days before his flight.

Serbia's Novak Djokovic arrived in Melbourne on January 5, beginning a protracted fight over his visa
Serbia's Novak Djokovic arrived in Melbourne on January 5, beginning a protracted fight over his visa POOL via AFP / Kelly Defina

The document spells out that "giving false or misleading information is a serious offence" and can result in being barred from Australia for three years.

In an airport interview on his arrival in Melbourne, Djokovic told border agents that his travel papers were filled in by his agent, according to a transcript released by the court.

There appears to be clear evidence that Djokovic did travel during that 14-day period.

He was pictured in Belgrade on December 25, with Serbian handball player Petar Djordjic. The photograph appeared on Djordjic's Instagram page.

On December 31, the SotoTennis academy tweeted a video of Djokovic training in Marbella, Spain.

"We can confirm that Novak Djokovic is ready for the Australian Open if possible," the academy tweeted -- at the time Djokovic had yet to commit to competing in Australia.

On January 2, Djokovic was pictured by the Diario Sur local newspaper playing at the Puente Romano club in Sierra Blanca, Marbella, where he was staying in a villa.

Djokovic arrived in Melbourne on January 5, only to have his visa was cancelled, beginning the legal fight that ended when a judge overturned that decision on Monday.

A spokesman for Australian Immigration Minister Alex Hawke said Tuesday he was "considering whether to cancel Mr Djokovic's visa" by using his ministerial powers.

But he would not comment further for legal reasons.