World No 1 Novak Djokovic is facing a backlash after Grigor Dimitrov tested positive for the coronavirus after his participation in the Serb's Adria Tour exhibition series.
"I want to reach out and let my fans and friends know that I tested positive back in Monaco for Covid-19," world No 19 Dimitrov wrote on Instagram.
"I am so sorry for any harm I might have caused. I am back home now and recovering."
Last weekend, Dimitrov, 29, took part in the Adria Tour event in Belgrade with Djokovic, world No 3 Dominic Thiem and Alexander Zverev, ranked seven.
He also played in the second leg of the Balkans tournament in Zadar on Croatia's Adriatic coast on Saturday.
However, he withdrew after losing to Borna Coric, complaining of feeling unwell.
Later on Sunday, the final between Djokovic and Russia's Andrey Rublev was immediately cancelled as a precaution.
"This is the best possible decision. We have to take care about security of all involved," former Wimbledon champion Goran Ivanisevic, the tournament director of the Zadar event, said in remarks quoted by local media.
"Those who were in contact with Grigor will be tested. I tested by chance three days ago and I'm negative."
Zverev and former US Open winner Marin Cilic were also in the Croatia line-up.
"I want to make sure anyone who has been in contact with me during these past days gets tested and takes the necessary precautions," Dimitrov said.
Djokovic's brother Djordje, who is the overall tournament director, told Sportske Novosti daily paper online edition: "Novak? He took this news very hard. We undertook all the measures prescribed by the governments of Serbia and Croatia."
However, Djokovic's remorse is not likely to save the 17-time Grand Slam champion from criticism.
The Adria Tour, organised to fill the gap in the virus-hit tennis calendar which has been on ice since mid-March, 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.
Dimitrov, Djokovic and Thiem, as well as the other players, were then seen partying at a packed Belgrade night spot.
Thiem has since travelled to the south of France to play in another exhibition tournament, the Ultimate Tennis Showdown in Nice.
On Sunday, tournament chief Patrick Mouratoglou, the coach of Serena Williams, tweeted a picture of Thiem undergoing a coronavirus test at the event being staged at his tennis academy.
The Adria Tour had already suffered an embarrassing setback when the planned Montenegro leg of the four-nation tournament was cancelled over coronavirus protocol rules.
Montenegro was due to be the third stop on June 27 and 28 after Croatia and before the conclusion in Bosnia. But organisers said the visit to Montenegro had to be called off when it became apparent Serbia did not match strict health requirements.
Meanwhile, asked to comment on social distancing measures during the Belgrade leg, Djokovic said both Serbia and the region had been relatively successful in containing the virus.
"Of course you can criticise, you can also say this is dangerous or not, but it's not up to me to make the calls what is health-wise right or wrong," he told reporters, stressing he was acting in line with recommendations of the Serbian government.
Djokovic's judgement was also questioned when he revealed he was opposed to vaccinations, even as the Covid-19 pandemic wreaked havoc around the world.
“Personally, I am opposed to vaccination, and I wouldn’t want to be forced by someone to take a vaccine in order to be able to travel,” he said in April.
Last week, the ATP and WTA said they were restarting their tours in August.
However, the US Open in New York will be played behind closed doors and under strict health protocols which Djokovic has described as "extreme" and "impossible".
The drama surrounding Dimitrov's test brought sympathy but also questions from fellow players.
"While watching images from the Adria Tour, I kind of felt that something was really wrong. Am I the only one? Is it a consequence of it? Get better soon Grigor," tweeted French player Alize Cornet.
Noah Rubin of the US added: "It's just not okay. Reckless and disappointing that they thought tennis deserved the risk."