Nick Kyrgios has ignited a war of words with Borna Coric after accusing the Croatian of having zero intellect following his passionate defence of the Adria Tour.

World No 40 Kyrgios has been quite vocal about his disapproval of the "boneheaded" decision to stage the Adria Tour during the coronavirus pandemic.

Four players, including Coric and world No 1 Novak Djokovic, tested positive for Covid-19 during the exhibition tournament in the Balkan region.

There has been plenty of back-and-forth mudslinging and Coric was the latest to hit out at Kyrgios, saying he is not interested in "lessons" from the 25-year-old.

And of course Kyrgios was never going to let it slide.

"You should care. Do you have rocks in your head?" the Australian said on Twitter.

"Again, you can stand up for your mates, I'm just trying to hold them accountable. They are tennis players, they aren't special.

"Just as I thought Coric intellectual level = 0."

- TEAMtalk media