Serbia's Prime Minister Ana Brnabićs comments on the tennis star following the rules came after it was alleged that Djokovic had attended a Belgrade Tennis Association event on December 17 and not worn a mask, the day after he tested positive to COVID-19 for a second time.

Ms Brnabić said Djokovic would have "clearly violated the rules" in place in Serbia, if had he known of the test result before he participated, before she added that additional clarification was needed.

"I don't know when he received the test result, when he read it," Ms Brnabić said.

When asked what would happen if Djokovic was found to have breached quarantine rules, she said the Serbian government would "deal with it".

"We will have an insight into that information because I think that information is part of the investigation that is currently led by the immigration ministry of Australia," she said.

"In the end, they made public a part of Novak's medical documentation, which I am not even sure was fair on their part to make it public, because it is not fair to make anyone's medical documentation public, unless they had Novak's explicit consent for that."

'Neither optimistic nor pessimistic'

Non-residents who are unvaccinated against COVID-19 cannot enter Australia unless they are exempted but Djokovic, who is not vaccinated, based his exemption on contracting the virus last month.

His visa was cancelled by Australian Border Force before Djokovic had that overturned in the Federal Circuit Court.

However the tennis star's fate remains in the balance as Immigration Minister Alex Hawke continues to consider whether to use his ministerial powers to cancel the Serbian star's visa.

If that happens, it could mean Djokovic is banned from entering Australia for three years, although ban periods are done on a case-by-case basis.

That investigation could involve whether or not Djokovic lied on his entry papers about his travel prior to coming to Australia.

Ms Brnabić, who had recently spoken with Australian Prime Minister Scott Morrison said she was "neither optimistic nor pessimistic" as to whether Djokovic will be permitted to stay in Australia, where he hopes to win a record 21st grand slam title.

"I hope that final decision will be announced soon," she told Reuters in an interview.

"Uncertainty is not good for any of the stakeholders, neither Djokovic nor the Australian Open."