Novak Djokovic, the men's world number one tennis player, has tested positive for COVID-19.
Croatia's Borna Coric, Grigor Dimitrov of Bulgaria and fellow Serb Viktor Troicki have previously tested positive after playing in Djokovic's Adria Tour exhibition tournament in the Balkan region.
Djokovic first played an event in Belgrade and then another in Zadar, Croatia.
His wife also tested positive, as did the wife of Troicki, who is currently pregnant.
"The moment we arrived in Belgrade we went to be tested. My result is positive, just as Jelena's, while the results of our children are negative," Djokovic said in a statement.
Djokovic, who has in the past expressed an anti-vaccination stance, has been criticised for organising the exhibition events and bringing in players from other countries amid the coronavirus pandemic.
That criticism continued on Tuesday night when Australian star Nick Kyrgios weighed in.
The Australian World number 40 — who has a history of clashing with the Serb — has been vocal about the tournaments that have been played and criticised those playing them.
Kyrgios tweeted his thoughts complete with a video that allegedly showed Djokovic and other players partying in Serbia after the exhibition event.
"Prayers up to all the players that have contracted Covid-19. Don't @ me for anything I've done that has been 'irresponsible' or classified as 'stupidity' — this takes the cake," Kyrgios tweeted.
At the tournaments he played there were no social distancing measures observed at the matches in either country, yet Djokovic defended holding the events.
"Everything we did in the past month, we did with a pure heart and sincere intentions," Djokovic said.
"Our tournament meant to unite and share a message of solidarity and compassion throughout the region.
"It was all borne with a philanthropic idea, to direct all raised funds towards people in need and it warmed my heart to see how everybody strongly responded to this.
"We organised the tournament at the moment when the virus has weakened, believing that the conditions for hosting the tour had been met."
The statement said Djokovic was showing no symptoms and he has said he will remain in self-isolation for 14 days.
He also apologised to anyone who became infected as a result of the series.
