Stefanos Tsitispas' father was branded "stupid" by French player Corentin Moutet during a heated exchange at the Ultimate Tennis Showdown (UTS).
Moutet said the Greek world number six's dad - and coach - Apostolos was talking when he was about to serve.
"It's not respectful," the world number 75 told commentators during the match.
"I won't speak about Stefanos, because he's a good guy. But it's just [his] father is stupid, everyone thinks he's stupid."
Tsitsipas did not seem too bothered by the argument, telling Moutet he would "not care" if the Frenchman's coach did the same.