Novak Djokovic on Wednesday admitted "errors" in his travel papers and for not isolating after a claimed coronavirus infection, as he battled to stay in Australia and fight for a record 21st Grand Slam.

The world number one said his team had offered fresh information to the Australian government, which is pondering whether to cancel his visa, again, and throw him out of the country.

"We are living in challenging times in a global pandemic and sometimes these mistakes can occur," the unvaccinated 34-year-old said in a statement released as he practised on the courts of the Australian Open, which starts Monday.

The Serbian star flew into Melbourne a week ago claiming a vaccine exemption because of a positive PCR test result on December 16.

Border agents rejected his exemption saying a recent infection did not qualify, tore up his visa and placed him in a detention centre.

But the vaccine-sceptic Djokovic's high-powered legal team dramatically overturned the visa decision in court on Monday on a procedural matter related to his airport interview.

Now, Immigration Minister Alex Hawke says he is considering cancelling the visa another time, as fresh doubts emerge.

In an update to Australian media, his spokesman acknowledged receiving "lengthy further submissions" from the player's lawyers.

"Naturally, this will affect the timeframe for a decision," he said.

- 'Error of judgement' -

Djokovic, a nine-time Australian Open champion, described reports about his post-infection outings in Serbia as "misinformation".

On the day of his claimed positive test in Serbia, he appeared at a ceremony to honour him with stamps bearing his image. The following day he attended a youth tennis event. He appeared at both apparently without a mask.

Djokovic, who made no mention of the stamp ceremony, said he only received the PCR test result after attending the children's tennis event.

But he admitted that he also went ahead with an interview and photoshoot with French sports newspaper L'Equipe on December 18.

"I felt obliged to go ahead and conduct the L'Equipe interview as I didn't want to let the journalist down but did ensure I socially distanced and wore a mask except when my photograph was being taken," he said.

"On reflection, this was an error of judgement and I accept that I should have rescheduled this commitment."

The player said he also had two rapid antigen tests, which both returned negative results: one on December 16 when he first suspected being infected and one on December 17 before attending the children's tennis event.

The tennis ace also admitted a mistake on his Australian travel declaration, in which a box was ticked indicating that he had not, or would not, travel in the 14 days before taking his flight to Melbourne.

In fact, social media posts and reports show he flew from Serbia to Spain during that period.

"This was submitted by my support team on my behalf," Djokovic said.

"My agent sincerely apologises for the administrative mistake in ticking the incorrect box about my previous travel before coming to Australia. This was a human error and certainly not deliberate."

In another twist, Australian media on Wednesday seized on reporting by Germany's Der Spiegel newspaper that cast doubt over the tennis star's positive test.

The newspaper said it had scanned the QR code on Djokovic's Serbian PCR test, which it said delivered a negative result, only to change to a positive result an hour later.

It was not possible to independently verify the Der Spiegel story, and Djokovic did not refer to those specific issues on Wednesday.

- Appeal options -

Djokovic's Instagram post appeared to be aimed at swaying the Australian government to let him stay.

Leading immigration lawyer Christopher Levingston said the government could cancel Djokovic's visa on narrow criminal grounds, for example, because the travel declaration was incorrectly completed.

But the immigration minister may also annul the visa on broader character grounds.

If Djokovic knowingly dodged Serbia's quarantine requirement for positive cases, he could be judged to be a risk for potentially not complying with public health orders while in Australia, Levingston said.

Various options to appeal would be open for both Djokovic and the government, but at the end of the day, the immigration minister can exercise his personal power to cancel the visa.

Many Australians, who have endured nearly two years of travel bans, restrictions and rolling lockdowns, were angered when they learned of Djokovic's vaccine exemption.

Prime Minister Scott Morrison's government, which faces a general election by May, has been criticised over its handling of the affair.

Meanwhile, the Women's Tennis Association said Wednesday that Czech player Renata Voracova did nothing wrong after she was detained on the same "unfortunate" grounds as Djokovic and deported from Australia.

Djokovic's visa ban was overturned only after the government conceded it had acted unreasonably by not giving him the promised time to put his case at the airport.

Since then, Djokovic's Covid-19 test and his actions before touching down in Australia have come under greater media scrutiny.