BRISBANE, Australia (AP) — Novak Djokovic had to spend a night at the Melbourne airport as officials refused to let him enter the country for the Australian Open after an apparent visa mix-up, leading Serbia’s president to blast the “harassment” of the top-ranked tennis player.

Djokovic flew in after receiving a medical exemption to play at the first Grand Slam tennis tournament of the season, where he is a nine-time winner and the defending champion. The exemption allows him to play regardless of his vaccination status for COVID-19, something he has not disclosed, but he also needs to meet strict border regulations to enter the country.

Australian media reported that Djokovic’s team had applied for the wrong type of visa for someone with a medical exemption. The issue had yet to be resolved more than eight hours after he landed Wednesday before midnight local time at Tullamarine Airport.

Djokovic’s father, Srdjan Djokovic, told the B92 internet portal that his son was held “in a room which no one can enter” at the airport, guarded by two policemen.

Djokovic’s participation in the Australian Open has become a hot political topic, with many Australians furious that he was granted an exemption to enter the country. Meanwhile, Serbian President Aleksandar Vucic said on Instagram that he has spoken to Djokovic and added that Serbian authorities are taking measures “so the harassment of the best tennis player in the world be stopped in the shortest possible time.”

Speculation of a possible issue with the visa emerged while Djokovic was in transit and escalated with mixed messages from federal and state lawmakers.

Djokovic’s revelation on social media that he was heading to Australia seeking a record 21st major title sparked some debate and plenty of headlines Wednesday, with critics questioning what grounds he could have for the exemption and backers arguing he has a right to privacy and freedom of choice.

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

The Victoria state government mandated that only fully vaccinated players, staff, fans and officials could enter Melbourne Park when the tournament starts Jan. 17.

Only 26 people connected with the tournament applied for a medical exemption and, Tiley said, only a “handful” were granted.

The names, ages and nationalities of applicants were redacted for privacy reasons before each application for a vaccine exemption was assessed by two independent panels of experts, and Tiley noted Djokovic is under no obligation to reveal his reason for seeking one.

But, he suggested, it would be “helpful” if Djokovic chose to explain it to a Melbourne public still getting over months of lockdowns and severe travel restrictions imposed at the height of the pandemic.

“I would encourage him to talk to the community about it,” Tiley said. “We have been through a very tough period over the last two years.”

The reasons allowed for a vaccination exemption can include acute major medical conditions, serious adverse reaction to a previous dose of a COVID-19 vaccine, or evidence of a COVID-19 infection within the previous six months.

Jaala Pulford, Victoria state’s acting minister for sports, acknowledged in the Djokovic case that lots of people in the community “will find this to be a disappointing outcome,” but added: “Nobody has had special treatment. The process is incredibly robust.”

Concerns about Djokovic’s visa status took a while to circulate.

Australian Prime Minister Scott Morrison initially said the medical exemption decision was a matter for the government of Victoria, where Melbourne is the state capital.

“They have provided (Djokovic) with an exemption to come to Australia, and so we then act in accordance with that,” Morrison said. “States provide exemptions for people to enter … and that’s been happening for the last two years.”

Home Affairs Minister Karen Andrews then clarified in a statement that the Australian Border Force would make the final determination.

“While the Victorian government and Tennis Australia 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,” Andrews said. “If an arriving individual is not vaccinated, they must provide acceptable proof that they cannot be vaccinated for medical reasons to be able to access the same travel arrangement as fully vaccinated travelers.”

When asked again about Djokovic’s case, Morrison added: “If that evidence is insufficient, then he won’t be treated any different to anyone else and he’ll be on the next plane home.”

“And so if medical exemptions had been provided by medical professionals and that’s been furnished to him as a proviso for him to get on that plane, well, that will have to stack up when he arrives in Australia,” the prime minister said.

Later still, Pulford, the Victoria state politician, posted on Twitter to say “the federal government has asked if we will support Novak Djokovic’s application to enter Australia.”

She said the state government would not be providing individual application support, adding in a second post: “We’ve always been clear on two points: visa approvals are a matter for the Federal Government, and medical exemptions are a matter for doctors.”

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

It’s possible that the 34-year-old Djokovic, who finished one win short of a calendar-year Grand Slam in 2021 when he lost the U.S. Open final to Daniil Medvedev, could have been infected again.