Novak Djokovic on Tuesday said he was "deeply sorry" after becoming the fourth tennis player to test positive for coronavirus following an exhibition tournament he hosted in the Balkans, admitting he and organisers "were wrong" to go ahead with the event.
The final leg of the Adria Tour in Bosnia has been cancelled and serious questions are being raised about the sport's planned official return in August.
Djokovic, who was not showing any symptoms, joined fellow players Grigor Dimitrov, Borna Coric and Viktor Troicki in testing positive for COVID-19 during the second leg of the event where social distancing was minimal, players were filmed dancing bare-top in a nightclub and embracing each other over the net.
World number one Djokovic said his wife Jelena also tested positive while the results of their children were negative.
"I am so deeply sorry our tournament has caused harm," the 33-year-old Serb, who has said he would be against a compulsory coronavirus vaccination if it became a requirement for tennis players to travel to tournaments, wrote on Twitter.
"We believed the tournament met all health protocols and the health of our region seemed in good condition to finally unite people for philanthropic reasons," the 17-time Grand Slam winner said, adding that he would now go into self-isolation for the next 14 days.
"We were wrong and it was too soon."
- Tournament cancelled -
Bulgaria's Dimitrov, the world number 19, announced on Sunday he had tested positive after pulling out of the event, the biggest since the tennis season was halted because of a pandemic that has killed over 470,000 people worldwide since it surfaced in China late last year.
Croatia's Coric and Troicki of Serbia followed suit on Monday, revealing they also had tested positive.
The final in the Croatian coastal town of Zadar was also cancelled Sunday.
The outbreak raises the question on how the ATP and WTA can best manage the restart of their tours scheduled for August.
It has already been established that the US Open in New York will be played behind closed doors and under strict health protocols which Djokovic, to much criticism, described as "extreme" and "impossible".
"Yikes... this is not good and it's a pattern..." tweeted female tennis legend Martina Navratilova after news of Djokovic's positive test.
"Hope Novak will be ok of course! What now, US Open? Roland Garros? We have a lot of work to do..."
The ATP, while wishing those infected a swift recovery, said Tuesday that it and other stakeholders had "made exhaustive plans to mitigate risks through a variety of precautions and protocols to be implemented at ATP events".
"We continue to plan and adjust these precautions and protocols according to latest medical information and prioritise safety in assessing every decision."
- No social distancing -
The cancellation of the Serbian star's Adria Tour has come on the back of a number of gaffes for Djokovic, who is the president of the ATP Player Council.
First criticised for breaking lockdown rules to train in Spain, he then invited derision for insisting emotions can change the quality of water while almost simultaneously insisting that he would not be prepared to vaccinate against coronavirus.
The Adria Tour's first stop had been played out to a daily crowd of 4,000 fans at Djokovic's tennis centre on the banks of the Danube in Belgrade last week, while a similar crowd attended the Zadar event.
Feliks Lukas, director of the WTA Croatia Bol Open, had warned against "incredibly bad" organisation in Zadar.
And local media reported that social distancing measures were respected by neither fans nor players in either venue. Djokovic was pictured playing basketball with Dimitrov and also embracing other players in the tournament.
Djokovic and other players including Belgrade winner Dominic Thiem were also seen partying at a packed night spot in the Serbian capital.
Thiem has since travelled to the south of France to play in another exhibition tournament in Nice, where his test came back negative.
Commenting on social distancing measures during the Belgrade leg, Djokovic argued that both Serbia and the region had been relatively successful in containing the virus.
But the Adria Tour had already suffered an embarrassing setback when the planned Montenegro leg of the four-nation tournament was cancelled when it became apparent Serbia's health requirements did not match up to those of Montenegro.
Australian tennis star Nick Kyrgios called it a "boneheaded decision to go ahead with the 'exhibition'", while Britain's Andy Murray called it "a lesson for all of us".