Sam Querrey left Russia on a private plane after he and his wife, Abby Dixon, tested positive for COVID-19 prior to the start of the St. Petersburg Open.
Per the Associated Press (h/t ESPN.com), tournament organizers said that Querrey and Dixon tested positive for the virus on Sunday and were placed in isolation by Russian authorities before leaving the country on Tuesday.
St. Petersburg Open organizers noted Querrey "did not open the door to doctors who came to examine the family on Monday, saying his baby son was sleeping, and the family then left the hotel before a second scheduled examination the next day."
In a statement to the AP, the ATP Tour said it was looking into a situation regarding COVID-19 protocols but didn't specifically 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. Adhering to health and safety protocols is critical to ensure events take place safely and within the guidelines established by local authorities. Players and their support team members are reminded that breaches of protocol can jeopardize 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."
Per Ben Rothenberg of the New York Times, Querrey and his family had been instructed to quarantine for 14 days but became alarmed when Querrey received a phone call from Russian health officials who said "the family would be visited by a doctor, and if they were found to have symptoms, they could be forced to be hospitalized."
Querrey was set to begin the tournament playing against Denis Shapovalov in the singles portion of the draw and play alongside Tennys Sandgren in doubles action before withdrawing because of his positive test.