Nick Kyrgios took a swipe at Borna Coric after the Croatian said he does not care about the Australian's criticism of Novak Djokovic's Adria Tour.
World number one Djokovic, Coric, Grigor Dimitrov and Viktor Troicki all tested positive for coronavirus at the exhibition event as social-distancing guidelines were ignored.
Alexander Zverev, who also featured, came under fire after he was apparently spotted partying despite saying he would quarantine for two weeks.
The outspoken Kyrgios criticised those who played at the event and branded Zverev "selfish".
Coric responded, telling Croatia's Jutarnji List newspaper: "I read what he wrote, but I simply don't care because he likes to be a general after a battle.
"If someone else was teaching lessons I would have understood, but Kyrgios...it's somehow not realistic.
"I agree that was not good, Zverev acted badly but I don't see the need to criticise fellow players in such a way. I wouldn't do it, but again, it's Kyrgios."
Kyrgios slammed the comments and said Coric's "intellectual level" is zero.
"You should care. Do you have rocks in your head?" Kyrgios, who added a donut emoji at the end of his post, wrote on Twitter.
"Again, you can stand up for your mates, I'm just trying to hold them accountable. When I said what I said, I didn't intend to bother.
"They are tennis players, they aren't special. Just as I thought, Coric intellectual level = 0."
