Benoit Paire has been withdrawn from the US Open after testing positive for coronavirus.
The Frenchman has been in New York for the best part of two weeks and had two negative tests when he first arrived, meaning he has contracted the virus while in the bio-secure bubble.
The 17th seed was due to play Poland's Kamil Majchrzak on Tuesday but has been withdrawn with no replacement in the draw announced yet. He is showing no symptoms but must isolate for 10 days.
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A USTA statement read: "A player has tested positive for Covid-19 at the US Open and has been withdrawn from the tournament. The player is asymptomatic.
"The USTA, together with its medical advisors and infectious disease specialist from the Mount Sinai Health System, confirmed a positive test result for a player.
"In accordance with New York State Department of Health requirements, and in alignment with CDC guidelines and the tournament health and safety protocols, the player has been advised that they must isolate for at least 10 days.
"In addition, contact tracing has been initiated to determine if anyone must quarantine for 14 days."
Paire took part in the Western & Southern Open at the same Flushing Meadows site last week, but retired during his first-round match against Borna Coric after feeling unwell, trailing 6-0 1-0.
Thiem feels 'super safe' despite US Open coronavirus shock
Dominic Thiem insists the US Open is the safest place in the world despite the tournament being rocked by the positive test on the eve of play.
"I think there is no safer place in the world right now than here," he said. "Maybe you can lock yourself somewhere in a cave or something, I don't know, in the middle of the sea. Otherwise it's super safe here. We are in a bubble.
"But still something can happen, as you could see with Benoit. We hope that nobody else is infected. In general, it's very, very safe and very strict."
British number one Johanna Konta admits the positive test is "worrisome" but is going about her business in the same manner ahead of her first-round encounter with compatriot Heather Watson on Tuesday.
"I mean, I just found out about five minutes ago," she said. "Obviously it's like, 'Oh wow, really?'.
"The issue we have is that it's not a full bubble and there are still some people who are working for the tournament, who are coming in and out. So, it's as safe as we can get in terms of how many people are here to run this operation.
"But it was always going to take us by surprise and be a bit shocking and worrisome if a player tested positive. Obviously we have had a few.
"It's definitely different when someone tests positive when they arrive or when they have been here, had negative tests and then test positive.
"It doesn't really change what I am doing on a day-to-day basis. Myself and the rest of the team are doing the best that we can in terms of keeping distance and trying to get on with our day-to-day things."
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