Australia has said it is investigating the visas of other foreign tennis players, after detaining Novak Djokovic in a chaotic row over vaccine rules.
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.
Ms Andrews added that the tennis star was not being held captive.