Novak Djokovic, the men's world number one tennis player, has tested positive for COVID-19, the Serbian said in a statement on Tuesday.
Croatia's Borna Coric, Grigor Dimitrov of Bulgaria and Viktor Troicki have previously tested positive after playing in Djokovic's Adria Tour exhibition tournament in the Balkan region.
"The moment we arrived in Belgrade we went to be tested," the 33-year-old said in a statement, adding that he was not showing any symptoms. "My result is positive, just as Jelena's (wife), while the results of our children are negative.
"I am extremely sorry for each individual case of infection. I hope that it will not complicate anyone's health situation and that everyone will be fine. I will remain in self-isolation for the next 14 days, and repeat the test in five days."
The tournament witnessed packed stands during the opening leg in Belgrade, players hugging at the net, playing basketball, posing for pictures and attending press conferences together.
Djokovic organised nights out in Belgrade for the players and pictures and videos of him dancing with the other participants at his event were posted on social media.
With both Serbia and Croatia easing lockdown measures weeks before the event, players were not obliged to observe social distancing rules in either country.
Djokovic said the idea behind his tournament was noble and he wanted to raise funds for players in need.
"Everything we did in the past month, we did with a pure heart and sincere intentions," said Djokovic, who is also the head of the players council of the men's ATP Tour. "Our tournament meant to unite and share a message of solidarity and compassion throughout the region.
"The Tour has been designed to help both established and up and coming tennis players from South-Eastern Europe to gain access to some competitive tennis while the various tours are on hold due to the COVID-19 situation."
A following statement confirmed that the remainder of the Adria Tour had been cancelled, the two-day event on July 3 and 4 in Banja Luka, Bosnia and the planned exhibition match with Bosnian Damir Dzumhur in Sarajevo on July 5.
"We are extremely disappointed to have to cancel the events in Banja Luka and Sarajevo," said Novak's brother Djordje Djokovic, the director of the Adria Tour.
"We were looking forward to treating fans in these two cities to watching Novak Djokovic and other top players. Unfortunately, the recent events make everyone’s speedy recovery a top priority."