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.”