Nick Kyrgios hit out at Alexander Zverev for being "selfish" after apparently being spotted partying despite vowing to self-isolate.
Zverev, the world number seven, played at the Adria Tour, where Novak Djokovic was among several players to test positive for coronavirus, as social-distancing guidelines were ignored earlier this month.
In a statement released on Twitter on June 22, Zverev said he tested negative for COVID-19 but would follow self-isolation rules, with 14 days usually recommended.
But the German was reportedly spotted partying and Kyrgios blasted the 23-year-old.
"So I wake up and I see more controversial things happening all over the world," Kyrgios said in an Instagram video.
"But one just stuck out for me was seeing 'Sascha' Zverev again, man, again, again, how selfish can you be? How selfish can you be?
"I mean if you have the audacity to f****** put out a tweet that you made your management write on your behalf saying you're going to self-isolate for 14 days and apologising to the f****** general public for 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, seriously, how selfish can you all get?"
The ATP Tour season is scheduled to restart in August, having been suspended in March due to COVID-19.
There have been more than 10.2 million confirmed cases of coronavirus worldwide, with the death toll exceeding 504,000.