American tennis star Sam Querrey, who had been placed in isolation by Russian authorities after testing positive for the coronavirus, has left the country with his family on a private plane.

Organisers of the St Petersburg Open said Querrey and his wife Abby had tested negative last Wednesday when they arrived in Russia with their baby son Ford but had then tested positive on Sunday, the day before main draw play started.

The world No.49 was withdrawn from the competition and the family was asked to isolate together at a hotel.

In a statement, the tournament said Querrey did not open the door to doctors who came to examine the family on Monday, saying eight-month-old Ford was sleeping, and the family then left the hotel before a second scheduled examination the next day.

“Sam Querrey, as the hotel’s security cameras identified, left the hotel together with his family at 5:45 a.m. on October 13 without informing the reception service. As Querrey told an ATP representative, he left Russia with his family on a private plane,” the tournament said, citing information from the ATP Tour.

The ATP said it was investigating an incident at the tournament, but did not name Querrey.

“The ATP is aware of an incident regarding a player’s serious breach of protocol relating to COVID-19 at this week’s St. Petersburg Open,” the tour said.

“Players and their support team members are reminded that breaches of protocol can jeopardise an event’s ability to operate and have repercussions on the rest of the Tour.

“In accordance with ATP’s Code of Conduct, we are taking this matter extremely seriously and an investigation is underway.”

There was no immediate comment from a spokesperson for the 33-year-old Querrey, a former Wimbledon semi-finalist.