Novak Djokovic was given no assurances that a medical exemption would allow him into Australia, lawyers fighting to deport the tennis star have argued, reports BBC.
The court filing by lawyers for the Australian government also reveal Djokovic, 34, is unvaccinated.
Australia's Covid border rules ban non-double vaccinated foreigners from entering, unless they have a medical exemption from having the jabs.
A court hearing is under way as Djokovic seeks to stop his deportation.
Djokovic's legal team argue a recent infection gives him a valid exemption.
The Serbian tennis player flew into Melbourne last week, hoping to defend his Australian Open title.
But instead he has been held in an immigration detention centre as his lawyers prepare to appeal against a decision by Australia's federal government to cancel his visa.
Tennis Australia has said it needs to know by Tuesday if he will be allowed to play, as it has to schedule his matches for the tournament, which begins 17 January.
On Saturday, Djokovic's lawyers submitted a 35-page document arguing that their client fulfilled the criteria for a vaccine exemption certificate because of a recent Covid infection, which was confirmed by a PCR test on 16 December.
But in Sunday's court filing, lawyers for Australia's home office dismissed this as a valid reason.
"There is no suggestion that the applicant had 'acute major medical illness' in December 2021. All he has said is that he tested positive for Covid-19. This is not the same," it said, adding there was "no such thing as an assurance of entry by a non-citizen into Australia".
It also said that "it is common ground" between the two parties that "the applicant is unvaccinated".
Djokovic has previously said he is opposed to vaccination, but never said openly whether he had had the vaccine.
In Australia, the news he had been granted a medical exemption was met with anger from citizens who have been living under some of the world's strictest Covid rules.
Those controls have separated families, and meant people missed funerals, births and weddings. Now that more than 90% of Australia's over-16 population are vaccinated some rules have been relaxed. However, some people still cannot travel interstate or globally because of current measures.
"I think it's a disgrace," Melbourne resident Christine Wharton told ABC earlier this week. "We've all done the right thing, we've all gone out and got our jabs and our boosters and we have someone that has come from overseas and all of a sudden he's been exempt and can play."