MELBOURNE, Australia — In a court filing on Saturday, lawyers for Novak Djokovic said the tennis star had tested positive for the coronavirus in mid-December, and that the Australian government had erred this week in canceling his visa over a vaccine requirement.

Mr. Djokovic, who hopes to defend his men’s singles title at the Australian Open this month, was denied permission to enter the country on Thursday after arriving at a Melbourne airport. The border authorities said they canceled his visa because he had not provided evidence to justify being exempted from Australia’s requirement that arrivals be vaccinated against the coronavirus.

In the filing on Saturday, Mr. Djokovic’s lawyers said he had been granted a vaccine exemption by Tennis Australia because of a positive Dec. 16 coronavirus test result, and because 14 days later, he had not had a fever or respiratory symptoms in 72 hours.

The conditions of the exemption were consistent with the recommendations of Australia’s immunization advisory body, the lawyers argued. Given these circumstances, among others, “Mr. Djokovic understood that he was entitled to enter Australia,” the filing read.

Mr. Djokovic, a vaccine skeptic, is in quarantine at a hotel in Melbourne as he awaits a hearing, scheduled for Monday, on his appeal of the government’s decision to revoke his visa.

He announced in June 2020 that he and his wife had tested positive for the coronavirus, but his December infection had not previously been disclosed.

Mr. Djokovic’s lawyers argue that the Australian authorities, in canceling his visa, “radically and fundamentally” misconstrued or misapplied advice from Australia’s immunization advisory body about whether a coronavirus infection within the past six months should exempt him from the vaccination requirement.

The filing also claims that Mr. Djokovic was denied procedural fairness after arriving in Australia, when he was held at the airport by the immigration authorities from about midnight to 8 a.m.

His lawyers say Mr. Djokovic was initially told by immigration officials that a decision about his visa would not be made until after 8.30 a.m., after he had a chance to speak to Tennis Australia officials. But around 6 a.m., they say, he was pressured to consent to an immediate decision. He relented, “feeling he had no choice,” and was notified at 7:42 a.m. that his visa had been canceled, according to the filing.

Australia’s Department of Home Affairs had no immediate response to the filing. Prime Minister Scott Morrison has said that the revocation of Mr. Djokovic’s visa was “simply a matter of following the rules.”

If Mr. Djokovic’s appeal fails, he could be barred from entering Australia for three years, under rules applicable to people whose visas are canceled.