Grigor Dimitrov announced Sunday he tested positive for COVID-19, one day after playing in Croatia as part of the Adria Tour.
"I want to make sure anyone who has been in contact with me during these past days gets tested and takes the necessary precautions," Dimitrov wrote on Instagram.
He added: "I am so sorry for any harm I might have caused. I am back home now and recovering. Thanks for your support and please stay safe and healthy."
The 29-year-old Bulgarian, who played against Borna Coric on Saturday, also appeared in the Serbian leg of the tour last week, which featured the likes of Novak Djokovic, Alexander Zverev, and Dominic Thiem.
The Adria Tour, an exhibition event organized by Djokovic, has had full crowds since it began this month. It's come under heavy criticism for potentially contributing to the spread of the novel coronavirus through a lack of physical distancing and necessary safety measures.
Shortly after Dimitrov's announcement, the tournament's final match between Djokovic and Andrey Rublev was suspended.
"At all times we have strictly followed the epidemiological measures in place with the countries where the Adria Tour was organized," read a statement from the Adria Tour. "None of the people involved in the organization and who have been in contact with Grigor have any symptoms. However, we are in close contact with health authorities in order to insure that all people who were in contact with Grigor Dimitrov will be tested tonight."
For his part, Djokovic has defended the staging of the event.
"I know there have been some criticisms, as well, especially coming from the West: 'Why do we have a crowd? Why not having social distancing? What is going on and why are they having this kind of event in the midst of a very hard pandemic in the West?'" Djokovic said on Eurosport's "Tennis Legends" podcast earlier this week.
He added: "But, you know, it's hard to explain to people that the situation is really, really different maybe in America or the U.K. than it is in Serbia or surrounding countries, and obviously from Day 1 of the organization of the Adria Tour, (we have been) following the rules and the measures that have been regulated by obviously the government institution and the public health institution."
The ATP Tour has been suspended since March due to the pandemic. Play is provisionally scheduled to return with the Citi Open in Washington, D.C., on Aug. 14. The WTA Tour is slated to resume on Aug. 3.