Australian tennis star Nick Kyrgios has taken aim at Novak Djokovic's “stupidity” after the world number one contracted coronavirus at an exhibition tennis tournament in the Balkans.

The final leg of the Adria Tour in Bosnia has been cancelled and Djokovic on Tuesday apologised for hosting the bungled event, admitting he and organisers “were wrong” to push ahead during the pandemic.

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 and players embraced over the net.

Kyrgios on Tuesday retweeted a video of players including Djokovic dancing shirtless in a nightclub, saying he sent “prayers” to the players who had contracted the virus.

“Don't @ me for anything I've done that has been 'irresponsible' or classified as 'stupidity' — this takes the cake,” he wrote.

The outspoken world number 40 has posted several Tweets criticising the event, and earlier called it a “boneheaded decision to go ahead with the 'exhibition'”.

“(T)hat's what happens when you disregard all protocols. This IS NOT A JOKE.”

The outbreak at the biggest tennis event since the pandemic began has prompted serious questions about the sport's planned official return in 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 described as “extreme” and “impossible”.

The ATP, while wishing those infected a swift recovery, said on 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”.