The tennis world was sent into a spin last week when several players returned positive coronavirus tests after taking part Novak Djokovic's Adria Tour event.

Zverev said at the time: "I deeply apologize (sic) to anyone that I have put at risk ... I will proceed to follow self-isolating guidelines."

The video of Zverev in Monte Carlo showed him clearly breaching social-distancing guidelines, prompting Kyrgios to lash the German star.

"So I wake up and I see more controversial things happening all over the world," Kyrgios posted on Instagram.

"But one that stuck out for me was seeing Sascha Zverev again, man, again, again. How selfish can you be?

"I mean, if you have the audacity to f------ put out a tweet that you make your management write on your behalf, saying you're going to self-isolate for 14 days and apologising to f------ the general public about putting their health at risk ... at least have the audacity to stay inside for 14 days.

"My God. Have your girlfriend with you for f------ 14 days. Jesus, man. Pissing me off ... this tennis world is pissing me off. How selfish can you all get?"

Zverev tested negative to coronavirus but said he would enter an isolation period.

"As an added precaution, my team and I will continue with regular testing," Zverev told fans.

Zverev's decision to go to a club has cast fresh doubt about the US Open going ahead in August, with the world still coming to grips with the coronavirus pandemic.

Kyrgios has emerged as the unusual voice of reason for players. The Canberra star has attracted criticism for his actions throughout his career, but he is winning respect by calling out those refusing to take the coronavirus spread seriously.

Kyrgios said the Djokovic's decision to host the event was "boneheaded". Djokovic, his wife and Grigor Dimitrov tested positive to COVID-19.

Djokovic said last week: "I am so deeply sorry our tournament has caused harm. Everything the organisers and I did the past month, we did with a pure heart and sincere intentions.

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"We believed the tournament met all health protocols and the health of our region seemed in good conditions to finally unite people for philanthropic reasons.

"We were wrong and it was too soon. I can't express enough how sorry I am for this and every case of infection."

Kyrgios' friend Andy Murray has also joined in criticism of the ATP tour, which is set to restart on August 14.

Murray believes the crammed new scheduled, which will see seven tournaments in as many weeks, will see players forced to skip major events.

The ATP tour, which was suspended in March due to the coronavirus outbreak, is set restart on August 14 with the Citi Open, followed by the Cincinnati Masters, which will be held at Flushing Meadows before the US Open.

The men's claycourt swing will start on September. 8 in Kitzbuhel followed by Masters tournaments in Madrid and Rome on September 13 and Rome Masters on September 20, with the French Open set to begin a week later.

"It's not safe for players to go from the semi-finals or final in New York... and then play in Madrid at altitude on clay when they haven't competed for a long time," Murray told a news conference during the 'Battle of the Brits' charity tournament.

"You're going to have the potential where a lot of top players are not competing at many of the biggest events."

The 33-year-old said with events coming thick and fast changes would need to be made with respect to players' ranking points.

"It might be worth looking at a two-year ranking for the time being maybe so that guys who have done well last year and are sort of not really able to defend their points properly aren't kind of punished," the twice Wimbledon champion said.

Murray suggested he will skip the tournament in Cincinnati to get his preparations for the US Open in order.

"I would rather play Washington and miss the event the week before at the US Open if they all go ahead," he added.

Murray returned to action following a seven-month injury lay-off at the charity event organised by his brother Jamie this week, progressing to the semi-finals before losing 1-6 6-3 10-8 to Dan Evans.