By AnneClaire Stapleton and Jessie Yeung, Jan 6 (CNN): Nine-time Australian Open champion Novak Djokovic may not be able to defend his 2021 title after his visa to enter Australia was cancelled following an outcry over his controversial "medical exemption" from the country's coronavirus vaccination rules granted by the competition's organizers.

Djokovic, the men's tennis world no.1 player, hasn't publicly revealed his vaccination status -- but in a news conference on Thursday, Australian Prime Minister Scott Morrison said he "didn't have a valid medical exemption" to the vaccination requirement for all arrivals.

"Entry with a visa requires double vaccination or a medical exemption," Morrison said. "I am advised that such an exemption was not in place, and as a result, he is subject to the same rules as everyone else."

"There are many visas granted, if you have a visa and you're double vaccinated you're very welcome to come here," he added. "But if you're not double vaccinated and you're not an Australian resident or citizen, well, you can't come."

Health Minister Greg Hunt said Thursday it was up to Djokovic whether he wanted to appeal the decision -- "but if a visa is cancelled, somebody will have to leave the country."

Djokovic's lawyers plan to challenge his deportation from Australia, and an appeal hearing is set to be heard Thursday evening, according to CNN affiliate Nine News -- however, his application to appeal the decision has not yet been submitted to the court.

CNN has reached out to lawyers believed to be representing Djokovic, the presiding judge over the appeal hearing and his agent, but have not yet heard back.

Djokovic has previously voiced opposition to compulsory Covid-19 vaccines, saying he was personally "opposed to vaccination" during a Facebook live chat. He contracted the virus in June 2020, but since then there have been no reports of him being re-infected.

The controversy comes as Australia faces a growing outbreak, has reported a record-high number of daily new cases for several days in a row.

Tournament organizers earlier said the Serb, who is trying to break the record for most men's grand slam singles titles, had received a medical exemption to play in the prestigious tennis tournament.

The exemption was met with controversy as Djokovic traveled to Melbourne on Wednesday.

He was reportedly being held at the airport after applying for a visa that does not permit medical exemptions for being unvaccinated for Covid-19, Australian news outlets reported.

According to The Age and The Sydney Morning Herald, the Australian Border Force (ABF) contacted the state Victoria government after learning of an issue with the visa submitted by Djokovic's team while he was en route to the country.

The ABF confirmed in a statement that the 34-year-old player's visa had been revoked for failing to provide appropriate evidence for entry to the country.

"The Australian Border Force will continue to ensure that those who arrive at our border comply with our laws and entry requirements," the statement read.

After the decision was confirmed, Morrison tweeted that Djokovic was subject to the same rules as everyone. "Rules are rules, especially when it comes to our borders. No one is above these rules. Our strong border policies have been critical to Australia having one of the lowest death rates in the world from COVID, we are continuing to be vigilant," he wrote.

Players were told they would have to be fully vaccinated in order to participate or have a medical exemption granted by an independent panel of experts.

The vaccine exemption sparked a backlash in Australia.

Deputy Victorian Liberal Leader David Southwick called the decision to allow Djokovic to take part in this year's tournament "a disgrace," describing it as a "kick in the guts to every Victorian" who endured months of lockdowns and suffered personal setbacks during the pandemic.

As events unfolded, Djokovic's father, Srdjan Djokovic, told a Serbian radio station his son was being held "captive" by Australian officials following a visa application mix-up.

He told Serbian radio station B92 his son was being housed in a room that no one can enter, with two policemen in the front of the room.

"I have no idea what's going on. They're holding my son captive for five hours," Srdjan Djokovic said in a statement to Russian news agency Sputnik, according to B92. "This is a fight for the libertarian world, this is not just a fight for Novak, but a fight for the whole world! If they don't let him go in half an hour, we will gather on the street. This is a fight for everyone."

Since the comments were made, there have been no reports of any gatherings in Belgrade or outside the Melbourne Airport.

Earlier on Wednesday, Djokovic's coach Goran Ivanisevic posted a photo to social media from what appears to be the Melbourne Airport in Australia where Djokovic reportedly was being held, captioning it, "Not the most usual trip Down Under."