Tennis legend Boris Becker has branded Nick Kyrgios a “rat” for calling out the antics of German ace Alexander Zverev.

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 him out on social media but Becker was none to happy with the Canberran’s takedown.

“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,” Becker tweeted on Tuesday night.

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.

Zverev had been widely condemned after being filmed dancing in a crowded room in Moncao, prompting Kyrgios to take the 22-year-old world No.7 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.