World number one Novak Djokovic has become the latest tennis player to test positive for Covid-19.
It comes after Grigor Dimitrov, Borna Coric and Viktor Troicki all revealed they had coronavirus after playing at Djokovic's Adria Tour competition.
Djokovic, 33, played fellow Serb Troicki in the first event in Belgrade.
Great Britain's Andy Murray said the positive tests were a "lesson for us", while Australian Nick Kyrgios called playing a "bone-headed decision".
A statement on Djokovic's website said: "Immediately upon his arrival in Belgrade [after the second event] Novak was tested along with all members of the family and the team with whom he was in Belgrade and Zadar. He is not showing any symptoms."
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There have been no ATP Tour events since February because of the global pandemic and the Adria Tour, which is not an ATP Tour event, was one of the first competitions to be staged since then.
The first leg in Serbia attracted 4,000 fans, and players were later pictured dancing close together in a Belgrade nightclub.
Bulgaria's Dimitrov played Croatia's Coric on Saturday in the second leg in Zadar, Croatia.
Bu bianca ecem
Bu bianca ecem
With Croatia easing lockdown measures, players were not obliged to observe social distancing rules and were seen embracing at the net at the end of their matches.
Pictures on the tournament's social media site from Friday showed Dimitrov playing basketball with Djokovic, Alexander Zverev and Marin Cilic, while he also put his arm around Coric before their match.