Videos emerged on Monday of Zverev partying in Monaco just days after being swept up in Novak Djokovic's Adria Tour debacle.

Zverev had pledged to self-isolate after featuring in the ill-fated tour that led to Djokovic, his wife, three more players and other members of their various entourage testing positive to coronavirus following a stint at a Belgrade nightclub.

A stunned Kyrgios labelled Zverev selfish and called the world No.7 out on social media.

But Becker was none too happy with the Canberran's take-down.

"Don't like no #rats ! Anybody telling off fellow sportsman/woman is no friend of mine! Look yourself in the mirror and think your better than us...@NickKyrgios @farfetch," Becker tweeted on Tuesday night.

"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 @farfetch."

Kyrgios was quick to strike back.

"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," he replied before following up with a second serve.

"Boris Becker is a bigger doughnut than I thought. Can hit a volley, obviously not the sharpest tool in the shed though."

The slanging match continued with Becker, a six-times grand slam champion and former world No.1, saying: 'Your funny guy ....how is it down under? Respect all the guidelines?"

"Haha nah bro I'm good, don't act like you're my friend now because you got sat down," Kyrgios tweeted.

Zverev had been widely condemned after being filmed dancing in a crowded room in Moncao, prompting Kyrgios to take the 22-year-old to task on Instagram.

"So I wake up and I see more controversial things happening all over the world, but one that stuck out for me was seeing Zverev again man, again, again, how selfish can you be? How selfish can you be?" Kyrgios said.

Australian Associated Press