Novak Djokovic's chance to play for a 10th Australian Open title was thrown into limbo Thursday when the country denied him entry and canceled his visa because he failed to meet the requirements for an exemption to COVID-19 vaccination rules.

The top-ranked Djokovic announced on social media Tuesday that he had "exemption permission" and he landed in Australia late Wednesday with a medical exemption from the Victoria state government that was expected to shield him from the strict vaccination regulations in place for this year's first major tennis tournament.

But national border authorities didn't accept the exemption, with the Australian Border Force issuing a statement saying Djokovic failed to meet entry requirements.

"The rule is very clear," Prime Minister Scott Morrison told a news conference. "You need to have a medical exemption. He didn't have a valid medical exemption. We make the call at the border, and that's where it's enforced."

Health Minister Greg Hunt said the visa cancellation followed a review of Djokovic's medical exemption by border officials who looked "at the integrity and the evidence behind it."

He said Djokovic was free to appeal the decision, "but if a visa is canceled, somebody will have to leave the country."

The president of Djokovic's native Serbia blasted the "harassment" of the star, who was detained overnight at Melbourne Tullamarine Airport. The 20-time major winner had to wait more than eight hours at the airport to find out if he would be allowed into the country. He was later moved to a secure hotel near downtown Melbourne which is controlled by immigration officials.

The Australian Broadcasting Corp. and other local media reported that action had been launched in the Federal Court against the cancellation of Djokovic's visa.

Quarantine-free access wouldn't have been an issue if Djokovic had been able to prove he was fully vaccinated for the coronavirus. Instead he applied for a medical exemption, a route that only became an option in recent months after Victoria state backed away from a full no-vaccination, no-play policy.

Questions have been raised about the approval of the exemption.

The Sydney Morning Herald published letters sent late last year from the Department of Health and Health Minister Greg Hunt to Tennis Australia which indicated that Djokovic, at that time, didn't meet the standard for quarantine-free entry.

Responding to questions about confusion over the differing state and federal requirements, Morrison said it was up to individual travelers to have correct documentation on arrival.

The prime minister rejected the suggestion that Djokovic was being singled out, but he acknowledged that other players may be in Australia on the same type of medical exemption.

"One of the things the Border Force does is they act on intelligence to direct their attention to potential arrivals," he said. "When you get people making public statements about what they say they have, and they're going to do, they draw significant attention to themselves."

Anyone who does that, he said, "whether they're a celebrity, a politician, a tennis player ... they can expect to be asked questions more than others before you come."

The medical exemptions, vetted by two independent panels of experts and based on information supplied anonymously by players and taken on face value, had been designed to allow Djokovic to play in the Australian Open, regardless of his vaccination status.

He has spoken out against vaccines in the past and has steadfastly refused to acknowledge whether he received any shots against the coronavirus.

His father, Srdjan Djokovic, told the B92 internet portal that his son was held at the airport "in a room which no one can enter" and guarded by two police officers.

Serbian President Aleksandar Vucic said on Instagram that he spoke to Djokovic while he was being held at the airport. He said Serbian authorities were taking measures "so the harassment of the best tennis player in the world be stopped in the shortest possible time."

Djokovic's revelation on social media that he was heading to Australia to seek a record 21st major title instantly became a hot political topic. Many Australians who have struggled to obtain sparsely available and often expensive rapid antigen tests, or who have been forced into isolation, perceived a double standard in the exemption allowance for Djokovic.

Critics questioned what grounds he could have for the exemption, and backers argued that he has a right to privacy and freedom of choice.

Tension is growing amid another surge of COVID-19. The state recorded six deaths and 21,997 new cases on Thursday, the biggest daily jump in cases in Victoria since the pandemic began.

Australian Open tournament director Craig Tiley on Wednesday defended the "completely legitimate application and process" and insisted there was no special treatment for Djokovic.

The Victoria government has mandated that only fully vaccinated players, staff members, fans and officials can enter Melbourne Park when the tournament begins Jan. 17.

Only 26 people connected with the tournament applied for a medical exemption and, Tiley said, only a "handful" were granted. None of those players have been publicly identified.

Among the acceptable reasons for an exemption are acute major medical conditions, serious adverse reaction to a previous dose of COVID-19 vaccine or evidence of a COVID-19 infection within the previous six months.

Djokovic tested positive for the coronavirus in June 2020 after he played in a series of exhibition matches that he organized in Serbia and Croatia without social distancing amid the pandemic.

Concerns about the visa status heightened Wednesday when Morrison—after initially saying it was a matter for the Victoria government—said if the evidence to support Djokovic's exemption application was deemed insufficient, "then he won't be treated any different to anyone else, and he'll be on the next plane home."

Home Affairs Minister Karen Andrews said while the state government and tennis organizers "may permit a non-vaccinated player to compete in the Australian Open, it is the Commonwealth government that will enforce our requirements at the Australian border."

Associated Press Writer Dusan Stojanovic in Belgrade, Serbia, contributed to this report.

Follow breaking news like this on our new platform, CHARISMA PLUS.

To contact us or to submit an article, click here.

Get Charisma's best content delivered right to your inbox! Never miss a big news story again. Click here to subscribe to the Charisma News newsletter.