Nick Kyrgios calls Boris Becker a ‘doughnut’ after being labeled a ‘rat’ by tennis great

The fallout from Novak Djokovic’s Adria Tour continues, with tennis great Boris Becker and current star Nick Kyrgios embroiled in a verbal tit-for-tat.

After a host of stars tested positive for Covid-19 after competing in the tournament – which attracted large crowds and where social distancing wasn’t in place – including Djokovic, his wife Jelena, three other players, three coaches and one player’s pregnant wife, the competition was canceled. Djokovic also issued a statement saying sorry the tournament “caused harm.”

One of the players who competed but tested negative, Alexander Zverev, announced on his social media that, despite his negative test, he would be self-isolating as a precaution. However, a video that emerged on social media a few days later appeared to show the German partying in a Monte Carlo nightclub.

READ: Novak Djokovic and the Adria Tour: the exhibition event that shocked tennis

Kyrgios, often the source of controversy in tennis, took to Twitter to criticize the 23-year-old Zverev, calling him “selfish” for ignoring social distance guidelines.

“If you have the audacity to f***ing put out a tweet, that you made your management write on your behalf, saying you’re going to self-isolate for 14 days and apologizing to the f***ing general public about putting their health at risk, at least have the audacity to stay inside for 14 days,” Kyrgios said on an Instagram story.

Kyrgios had previously called the decision to host the Adria Tour as “boneheaded.” Zverev’s management team did not immediately respond to CNN Sport’s request for comment.

‘Don’t like no #rats!’

However, Djokovic’s former coach Becker has described Kyrgios as a “rat” on Twitter for calling out Zverev’s behavior.

“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,” Becker said.

In reply, Kyrgios said: “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.”

Becker then doubled down, saying: “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.”

Kyrgios clearly didn’t appreciate being called a “rat” by Becker.

“Rats? For holding someone accountable? Strange way to think of it champion, I’m just looking out for people,” the 25-year-old Australian said.

“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.”

Later, Kyrgios went on to call the three-time Wimbledon champion a “bigger doughnut than I thought” and “obviously not the sharpest tool in the shed.”

Kyrgios has also been vocal in his criticism about the rescheduled US Open, which is currently set to take place between August 24 to September 13.

Visit CNN.com/sport for more news, features, and videos

“People that live in the US of course are pushing [for] the Open to go ahead. ‘Selfish,’” he wrote on Twitter. “I’ll get my hazmat suit ready for when I travel from Australia and then have to quarantine for 2 weeks on my return.”