Sam Querrey left Russia on a private jet after testing positive for Covid-19 at the St Petersburg Open, according to tournament organisers.
The American was a late withdrawal from the event after he tested positive, along with his wife and baby son.
The tournament organisers, Formula TX, say Querrey was "isolated in a Four Seasons hotel room". However, when they arranged for a doctor to visit Querrey they were unable to gain entry to the room and the family then left the hotel the next day without informing reception.
"As Querrey told the ATP representative, he flew out of Russia on a private jet,” organisers Formula TX said in a statement.
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"The ATP representative passed on this information to the tournament management after the doctors made a repeat abortive attempt to examine the family.
"The tournament organising committee has done it all to ensure the safety of the players, the ATP representatives and all the services of the tournament.
"It is the power of the ATP to evaluate and assess the actions of the player Sam Querrey."
The ATP on Wednesday released a statement to its players saying a "serious breach of protocol" had occurred at the tournament, but did not name Querrey.
Additional reporting by Reuters