Kyrgios called out German tennis star Alexander Zverev on Monday after he was spotting at a club in the French Riveria.
Zverev played at Novak Djokovic's Adria Tour in Belgrade and Croatia earlier this month which led to four competitors contracting coronavirus.
Zverev claimed he would “follow self-isolating guidelines” but apologised when footage emerged of him in the club.
“No matter how lazy, sloppy and selfish players are about following public health guidelines mid-pandemic, they sure can spring to quick action to cover their asses,” respected tennis journalist Ben Rothenberg said.
Zverev tested negative to coronavirus last week, but Kyrgios was quick to slam the behaviour.
“Sascha Zverev again, man. Again, again, how selfish can you be?” Kyrgios said.
“If you have the audacity to 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 general public about putting their health at risk, at least have the audacity to stay inside for 14 days.
“Jesus, man. P***ing me off. This tennis world is p***ing me off, seriously. How selfish can you all get?”
Becker quickly jumped to Zverev's defence, calling Kyrgios a “rat”.
“Don’t like no rats! Anybody telling off fellow sportsman/woman is no friend of mine!” Becker posted to Twitter on Tuesday.
“Look yourself in the mirror and think your (sic) better than us.”
Kyrgios defended his comments.
“For goodness sake Boris, I’m not competing or trying to throw anyone under the bus,” the 25-year-old replied.
“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.”
However, Becker continued to call Kyrgios a “rat”.
“We all live in the pandemic called COVID-19! It’s terrible and it killed to many lives,” the German posted. “We should protect our families/loved ones and follow the guidelines but still don’t like rats.
“(Zverev) broke the quarantine rules and he should be ashamed of himself! He is a role model for many tennis fans a bright star on the horizon but still don’t like rats.
“There is an unspoken understanding between athletes! Whatever happens on the court stays there including the lockers! Nobody will talk about it.”
Kyrgios continued to hold firm and poked fun at Becker.
“Rats? For holding someone accountable? Strange way to think of it champion, I’m just looking out for people,” Kyrgios tweeted.
“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.
After receiving massive backlash on Twitter for his remarks, Becker joked with Kyrgios.
“Your funny guy … how is it down under? Respect all the guidelines?”
Kyrgios wasn't having any of it and bluntly replied.
“Haha nah bro I’m good, don’t act like you’re my friend now because you got sat down.”
This isn't the first time Kyrgios has called someone out, as he slammed Novak Djokovic and his wife for their “boneheaded decision” to organise the tournament during a pandemic.
“Prayers up to all the players that have contracted COVID-19,” Kyrgios tweeted last week.
“Don’t @ me for anything I’ve done that has been ‘irresponsible’ or classified as ‘stupidity’ — this takes the cake.”
This article originally appeared on Over60.