Nick Kyrgios has accused world number one Novak Djokovic of lacking "leadership and humility" after he and fellow competitors tested positive for coronavirus earlier this summer.
His comments came after Djokovic, who is currently playing at the Western and Southern Open in New York, had been asked about the possibility of going through 2020 unbeaten after a 20-0 start to the year.
In a post on his official Twitter account, 25-year-old Australian Kyrgios said: "Hell of a tennis player. May go unbeaten in 2020, can't take that away from him.
"Unfortunately when he was supposed to show some leadership and humility he went missing. Majority would say he has taken an L regardless."
Djokovic, Grigor Dimitrov, Borna Coric and Viktor Troicki all returned positive tests after taking part in the Adria Tour, a tournament organised by the 17-times Grand Slam winner in June.
The opening leg of the event took place at the 33-year-old's tennis complex in Belgrade and the second in Zadar in Croatia.
Although the tournament did not breach any official protocols in Serbia or Croatia, Djokovic was heavily criticised after players hugged at the net, posed for photographs and attended joint press conferences.
The reigning Wimbledon champion and his wife Jelena, who had also tested positive, returned negative results nine days later after self-isolating.
Djokovic later apologised and insisted the event had been organised with the best of intentions.
