Australia has said it is investigating the visas of other foreign tennis players, after detaining Novak Djokovic in a chaotic vaccine row.
The men's world number one remains in immigration detention in Melbourne and is facing deportation after his entry to the country was denied on Wednesday.
He has launched an urgent court challenge to be heard on Monday, a week before the Australian Open begins.
Now more uncertainty surrounds the tournament schedule.
In an interview, Home Affairs Minister Karen Andrews said there was intelligence to "indicate there are some individuals here now that have not met the entry requirements and we have to investigate that," she told Channel 9 on Friday.
However, she did not say how many other players were under investigation or who they were.
Djokovic, who has said he is opposed to vaccination, had been granted a medical exemption to play in the tournament for unspecified reasons, a decision that infuriated many Australians.
The exemption was given by two independent medical panels organised by Tennis Australia, the body that runs the event, and Victoria state, tournament organisers said.
But on Wednesday, Australian Border Force (ABF) officials said the 34-year-old Serbian player had "failed to provide appropriate evidence" at Melbourne Airport.
"If he hasn't filled out the forms appropriately then he's taking the sovereign capacity of another nation for a joke," Deputy Prime Minister Barnaby Joyce told the BBC's Newshour programme.
"100% someone's made a mistake and if he hasn't told the truth then the person who's made the mistake is Djokovic."
The federal government has criticised Tennis Australia for ignoring ABF advice about the requirements for entry. On Friday, Victoria said Tennis Australia had also failed to pass on this advice.
Prime Minister Scott Morrison is also being accused of politicising the issue. The prime minister himself is under pressure amid the surge of Covid-19 infections in the country, and a federal election is likely to be held in May.
The row prompted Serbian President Aleksandar Vucic to say Djokovic was a victim of "harassment" and that "the whole of Serbia" supported him.
Morrison has denied the visa cancellation was because of "any particular position in relation to Serbia".
It is not yet clear how long Djokovic will remain in an immigration detention hotel that has often been criticised by refugees for its poor conditions.
Djokovic's wife, Jelena, thanked people "all around the world for using your voice to send love to my husband".
The player's father, Srdjan, said his son had been held in a room guarded by police at the airport, adding that it was "not just a fight for Novak, but a fight for the whole world".
But others such as Spanish tennis start Rafael Nadal, who is in Melbourne to prepare for the tournament, said it was "normal" for Australians to get "very frustrated with the case".
"The only for me clear thing is if you are vaccinated, you can play in the Australian Open," he said, adding: "Of course after a lot of people had been dying for two years, my feeling is
the vaccine is the only way to stop this pandemic."The Australian Open begins on 17 January. Djokovic has previously won the tournament nine times.
