American Sam Querrey left Russia two days after testing positive for coronavirus at the St Petersburg Open, say tournament organisers.
The world number 49 was removed from the event on Monday after he, his wife and baby son contracted the virus.
Querrey, 33, left the country on a private jet instead of quarantining.
"As Querrey told an ATP representative, he and his family left Russia on a private plane," a statement on the tournament website said.
Querrey and his wife passed their initial coronavirus test upon arrival at the tournament on 7 October, but tested positive four days later.
The event's organisers say the former Wimbledon semi-finalist was "isolated in a Four Seasons hotel room".
When they arranged for a doctor to visit Querrey, they were unable to gain entry to his room on two occasions.
The tournament's organising committee then arranged for a private apartment for the family but say it went unused as Querrey left the hotel on Tuesday.
The statement continued: "Sam Querrey, as recorded by hotel surveillance cameras, at 5.45am on 13 October, along with his family without notifying reception, left the hotel."
The ATP - the men's tour's governing body - declined to comment publicly but sent an email to players following the incident calling it "a serious breach of protocol" and adding "we are taking this matter extremely seriously and an investigation is under way".
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