By Sonali Paul and Cordelia Hsu

MELBOURNE:Novak Djokovic on Tuesday warmed up for his bid to win a record 21st Grand Slam title at next week's Australian Open, hitting practice shots at Melbourne Park, but he still faces the threat of deportation.

A week after his arrival in Australia, Djokovic finally reached the tennis court after a judge on Monday quashed the federal government's decision to cancel his visa.

But the world number one could still be detained by the federal government for a second time and deported. Immigration Minister Alex Hawke's office said he was considering whether to use his discretionary power to cancel Djokovic's visa.

Australia has a policy barring non-citizens or non-residents from entry unless they are fully vaccinated against COVID-19. It allows for medical exemptions but the government argued that Djokovic, who is not vaccinated, did not provide adequate justification for an exemption.

The court ruled Djokovic was treated unfairly by officials on his arrival and ordered his visa cancellation be overturned. It did not, however, address whether his exemption - based on Djokovic contracting COVID-19 last month - was valid.

Djokovic's case provoked a row between Canberra and Belgrade and fuelled heated debate over mandatory COVID-19 vaccination policies.

Public opinion in Australia, which is battling an Omicron wave of infections and where more than 90% of the adult population is double vaccinated, has been largely against the player.

Melbourne endured the world's longest coronavirus lockdown and Victoria state has Australia's highest number of COVID-19 deaths.

Prime Minister Scott Morrison's office said he spoke with Serbian Prime Minister Ana Brnabic on Monday and explained Australia's non-discriminatory border policy.

In an interview with Reuters, Brnabic said she felt neither optimistic or pessimistic over to whether Djokovic would be allowed to compete but hoped for a final decision soon.

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

The ATP, the governing body of men's tennis, applauded the court ruling, saying the dispute was "damaging on all fronts."

Djokovic, who expressed his gratitude to the judge and his determination to compete at the first major of the year in a Twitter post on Monday, did not publicly address the situation on Tuesday.

He was filmed by media helicopters practicing at Rod Laver Arena amid tight security at Melbourne Park. He was also confirmed as top seed for the event.

OPPOSITION TO VACCINATION

Djokovic was detained when he landed at Melbourne airport last Wednesday. His visa was cancelled because he failed to provide appropriate evidence to meet entry requirements, border officials said.

However, in quashing that decision Judge Anthony Kelly was critical of the hours-long airport interview and said the player had not been given enough time to contact lawyers and tennis officials to discuss his predicament.

Djokovic had been granted a medical exemption by the Victoria state government based on evidence he contracted COVID-19 last month - the second time he had been infected. The player, who has long opposed mandatory vaccination, confirmed during the interview he was unvaccinated.

Some Australian media reported that Australian Border Force was investigating potential discrepancies in the traveller form submitted by Djokovic and his whereabouts in the days before he arrived in Australia.

In the document submitted to court Djokovic ticked "no" when asked he had been overseas in the 14 days prior. Social media posts, however, appeared to show him in Belgrade on Christmas Day and in Spain on Dec. 31.

In Madrid, Spain's foreign minister said he had no information on whether Djokovic had visited Spain in December before travelling to Australia.

"We have not been contacted by the Australian government to request such documentation," Minister Jose Manuel Albares also said.

The Australian Border Force did not reply to a request for comment. Djokovic's lawyers at Hall & Wilcox declined to comment.

FAIREST DECISION, SAYS RAFA

The Australian Open begins on Jan. 17. Djokovic has won the tournament, one of four tennis Grand Slams, for the past three years and nine times in all.

Spain's Rafa Nadal, who is tied on 20 majors with Djokovic and Switzerland's Roger Federer, called the fraught build-up to the tournament a "circus" and said the "fairest decision" had been made.

Nick Kyrgios said while he supported vaccination he felt "embarrassed as an Australian athlete, seeing what this guy has done for us and the sport".

However, former American player turned pundit Pam Shriver warned on Twitter the controversy may not be over: "If he plays the booing will be deafening."

Melbourne resident Keith Moore told Reuters: "We've had to go through vaccination protocols and lockdowns for such a long time and he swans in and pretty much does what he likes because he's the world best tennis player."