Grigor Dimitrov said on Sunday said he has tested positive for COVID-19, making him the highest-profile tennis player to reveal he has the disease.
The 29-year-old Bulgarian had been competing in the Adria Tour exhibition tournament in Croatia until he withdrew with illness during the weekend.
The final of the event, which would have featured world No. 1 Novak Djokovic and Russian Andrey Rublev, was cancelled as a result.
"I want to reach out and let my fans and friends know that I tested positive back in Monaco for COVID-19," former world number three Dimitrov wrote on Instagram.
"I want to make sure anyone who has been in contact with me during these past days gets tested and takes the necessary precautions.
"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 second leg of the Adria Tour, a Balkan charity event organised by Djokovic while international tennis remains suspended due to the COVID-19 pandemic, was taking place in Zadar, Croatia.
"We have just been informed that Grigor Dimitrov has tested positive for coronavirus and we will have to call off the final of the tournament in Zadar," Djokovic's coach and the event's director Goran Ivanisevic told fans courtside.