Nick Kyrgios and Boris Becker traded insults on social media on Tuesday following the Australian's criticism of Alexander Zverev after a video appeared to show the German dancing in a crowded club despite the coronavirus pandemic.
The video was posted on Instagram by German designer Philipp Plein and later deleted. There was no indication of when the video was taken.
Zverev said last week he would self-isolate after playing in Novak Djokovic's ill-fated Adria Tour exhibition tournament in Serbia and Croatia, which had to be abandoned after numerous players tested positive for the coronavirus.
Kyrgios on Monday called Zverev, the men's world No. 7, "selfish," prompting a rebuke from commentator and former six-time Grand Slam champion Becker.
"We all live in the pandemic called #Covid_19! It's terrible and it killed to many lives...we should protect our families/loved ones and follow the guidelines but still don't like #rats @NickKyrgios," Becker said on Twitter.
Kyrgios was prompt in his reply: "Rats? For holding someone accountable? Strange way to think of it champion, I'm just looking out for people. When my family and families all over the world have respectfully done the right thing. And you have a goose waving his arms around, imma say something.
"For goodness sake Boris, I'm not competing or trying to throw anyone under the bus. It's a global pandemic and if someone is as idiotic as Alex to do what he has done, I'll call him out for it. Simple."
Zverev, 23, took part in Djokovic's event, which saw crowds packed into stands in Belgrade while players hugged at the net and played basketball in Croatia. The German player said he and his team had tested negative.
The Australian continued: "@TheBorisBecker is a bigger doughnut than I thought ... can hit a volley, obviously not the sharpest tool in the shed though."
Why are you now talking about tennis? It has nothing to do with tennis? How about the dude who you are defending mans up and gives us some sort of explanation? Not another average management apology.
— Nicholas Kyrgios (@NickKyrgios) June 30, 2020
Becker responded: "I really would like to see @NickKyrgios fulfill his potential and win a grand slam! He would be an incredible role model for for the youth of the world addressing the issues of equality/race/heritage! Man up buddy and deliver!"
Kyrgios came back and said: "Why are you now talking about tennis? It has nothing to do with tennis? How about the dude who you are defending mans up and gives us some sort of explanation? Not another average management apology."
Kyrgios had previously criticised the organisers of the Balkan event and hit out at governing bodies for their plans to restart professional tennis during the pandemic.