American Frances Tiafoe has become the latest tennis player to test positive for coronavirus.
The world number 81 had been playing in the All-American Team Cup in Georgia, the first event in the US to allow fans to attend since the Covid-19 shutdown.
Tiafoe, 22, won his match on Friday but confirmed his withdrawal from the tournament on social media on Saturday.
Novak Djokovic, Grigor Dimitrov, Borna Coric and Viktor Troicki contracted the virus playing in Belgrade last month.
Tiafoe, a quarter-finalist at the 2019 Australian Open, had tested negative last week and said: "I am scheduled to have a second test early next week, but have already begun the quarantine protocol as advised by the medical staff here in Atlanta.