An unnamed player, widely reported to be Frenchman Benoit Paire, has been withdrawn from the US Open after testing positive for coronavirus.
The player is showing no symptoms but must now isolate for 10 days.
A USTA statement said: "A player has tested positive for COVID-19 at the US Open and has been withdrawn from the tournament.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, the 17th seed, was due to play Poland's Kamil Majchrzak on Tuesday. His replacement in the draw has yet to be announced.
The Frenchman has been in the bio-secure bubble in New York for a couple of weeks and took part in the Western & Southern Open at the same Flushing Meadows site last week.
However, he retired during his first-round match against Borna Coric after feeling unwell, trailing 6-0 1-0.