Contact tracing has been launched to determine if anyone else needs to quarantine for 14 days due to the presence of the player involved.
The shock comes after players trained and played a tune-up event, the ATP and WTA Western and Southern Open typically held in Cincinnati, in the same quarantine bubble where the US Open begins Monday without spectators.
Pair, 31, made his first Grand Slam fourth round in 2015 at the US Open and it stays on par for his deepest slam run.
Paire, seeded 17th, was due to play his first US Open game against Kamil Majchrzak, 108th from Poland.
USTA officials are not supposed to confirm the test results of an individual player under US medical privacy laws.
World number one Novak Djokovic is the man to beat as he pursues an 18th Grand Slam title and fourth crown on the New York courts after 2011, 2015 and 2018.
Serena Williams will look to win her 24th career Grand Slam women’s singles crown to equal Margaret Court’s all-time record.
Djokovic and Japan’s Naomi Osaka, whose status is uncertain due to a left hamstring injury that forced her to withdraw from Saturday’s WTA New York final, are both expected to play in the games of monday night background.