World tennis number one Novak Djokovic tweeted a picture of himself practicing at Melbourne's Rod Laver Arena hours after winning a court challenge on Monday to remain in Australia.

The fight over his medical exemption from COVID-19 vaccination may not be over, however, as the Australian government said it was still considering another move to deport him.

"I am pleased and grateful that the judge overturned my visa cancellation," Djokovic wrote on Twitter. "Despite all that has happened I want to stay and try to compete at the Australian Open."

Earlier Judge Anthony Kelly had ruled the federal government's decision last week to revoke the Serbian tennis star's visa amid was "unreasonable" and ordered his release.

Kelly reinstated Djokovic's visa, which was revoked after his arrival last week because officials decided he didn't meet the criteria for an exemption to an entry requirement that all non-citizens be fully vaccinated.

The judge ruled the No. 1 player had not been given enough time to speak to his lawyers before that decision was made and ordered the government to release him within 30 minutes from a Melbourne quarantine hotel where he has spent the last four nights.

But government lawyer Christopher Tran told the judge that the immigration minister will consider whether to exercise a personal power of cancellation.

That would mean that the nine-time Australian Open winner and defending champion could again face deportation and could miss the tournament, which starts on Jan. 17. It could also bar him from the country for three years.

The back and forth has gripped the world and caused a furor in Australia, where many initially decried the news that Djokovic, who has been a vocal skeptic of vaccines, had received an exemption to strict rules to compete in Melbourne. Many felt the star was being given special treatment since Australians who aren't vaccinated face tough travel and quarantine restrictions. Court documents say he is unvaccinated.

But when border police then blocked him on arrival, others cried foul, saying he was being scapegoated by an Australian government facing criticism for its recent handling of the pandemic.

Speaking with television network Prva in Belgrade, Serbia, the tennis star's brother, Djordje Djokovic, described the judge's ruling as a great defeat for Australian authorities.

But he said the family was still hearing that his brother might be detained, though he gave no details.

This is definitely politics, all this was politics, he added.

The office of Home Affairs Minister Karen Andrews confirmed that Novak Djokovic has not been arrested. It was not clear where he was, though hundreds of fans gathered late Monday outside his lawyers' office in Melbourne, many carrying Serbian flags and wearing the banner's red, white and blue colors. They chanted Free Nole, using the star's nickname. Police later dispersed them when they surrounded a car trying to leave the area.

The 34-year-old Djokovic boarded a plane for Australia last week, after receiving an exemption from vaccination rules from Victoria state authorities and Australian Open organizers. But upon arrival, federal border officials refused to let him, saying the exemption was not valid.

The reversal, in the wake of the outcry, led some to suspect politics were at play, with Prime Minister Scott Morrison's conservative government seeking re-election for a fourth term in polls due by May.

While his government was widely praised for containing the nation's COVID-19 death toll at the start of the pandemic, he has recently loosened some rules, just as omicron cases have been rapidly surging. He has been criticized for that strategy as well as for shortages of rapid antigen tests and for refusing to make the tests available to all for free.

Lawmaker John Alexander, a former tennis professional, said a move by the immigration minister to personally intervene would be unfair.

The Minister's personal powers to cancel visas' are designed to prevent criminals otherwise walking our streets, or to prevent a contagious person otherwise walking our streets; they're not designed to assist in dealing with a potential political problem of the day, Alexander, who is in Morrison's conservative Liberal Party but is retiring, posted on social media.

At Monday's court hearing, Djokovic's lawyers argued their client did not need proof of vaccination because he had evidence that he had been infected with the coronavirus last month.

Australian medical authorities have ruled that people who have been infected with COVID-19 within six months can receive a temporary exemption to the vaccination rule.

Judge Kelly noted that Djokovic had provided officials at Melbourne's airport with a medical exemption given him by Tennis Australia and two medical panels.

The point I'm somewhat agitated about is what more could this man have done? Kelly asked Djokovic's lawyer, Nick Wood.

Wood agreed that his client could not have done more.

Transcripts of Djokovic's interview with Border Force officials and his own affidavit revealed a repeated appeal to the officers with which he was dealing that to his understanding, uncontradicted, he had done absolutely everything that he understood was required in order for him to enter Australia, Wood said.

Djokovic's lawyers described the cancellation as seriously illogical.

But lawyers for Home Affairs Minister Andrews said in their submission that the vaccination exemption could only be granted for travelers who had recovered from a serious bout of COVID-19.

There is no suggestion that the applicant (Djokovic) had acute major medical illness' in December when he tested positive, the written submission said.

But in the end, the government lawyers eventually conceded that the decision to proceed with interviewing Djokovic in the early hours of Thursday and cancel his visa before he could contact Tennis Australia or his lawyers was unreasonable.

Djokovic was told at 5.20 a.m. on Thursday that he had until 8.30 a.m. to respond to a notice of intention to cancel his visa. His comments were sought instead at 6.14 a.m.

The decision to cancel his visa was made just over an hour later.

Minister Andrews did not immediately responded to a request for comment. But a spokesperson for Alex Hawke, minister for immigration, citizenship, migrant services and multicultural affairs, acknowledged the court's decision, adding the minister's personal discretion remains in play.

The minister is currently considering the matter and the process remains ongoing, the spokesman said.

The virtual hearing crashed several times because of an overwhelming number of people from around the world trying to watch the proceedings.

At one point, an expired court link was apparently hacked and broadcast pornography, The New Daily News website reported.

Djokovic has 20 Grand Slam singles titles, a men's record he shares with Roger Federer and Rafael Nadal.