A number of US Open players have been put in what one described as "a bubble in the bubble" after having contact with France's Benoit Paire, who tested positive for coronavirus.
Compatriot Kristina Mladenovic says her movements have been restricted as she was in a group of players who played cards with Paire in a hotel lobby.
Mladenovic, who won her first-round match on Monday, said she had not been sure if she would be allowed to play.
She and the others will do daily tests.
"We got some bad news a couple of days ago and since then for me it was kind of a nightmare," 30th seed Mladenovic said in an on-court interview after her 7-5 6-2 win over Hailey Baptiste.
"I wasn't sure if I will be able to play here and I've been myself put out of the bubble - a sort of bubble within the bubble - so I'm just very grateful I can be on the court today and safe, to get the win is amazing and I didn't expect that."
On Sunday, French number 17 seed Paire was replaced in the men's singles draw by Spain's Marcel Granollers at the behind-closed-doors Grand Slam.
Organisers, the US Tennis Association (USTA), have not named Paire but the player wrote on social media on Monday that he feels "fine for the moment" and has no symptoms.
The USTA said in a statement: "At this point we will not be withdrawing any other player in the tournament.
"We will continue to work closely with the DOH [Department of Health] in all matters, including contact tracing, as we always have. We remain with just one player positive test, and one non-player positive test out of 7,995 tests."
The USTA added it has placed an unspecified number of players in what it describes as an "enhanced protocol plan".