Barcelona coach Hansi Flick accused Jude Bellingham of being "disrespectful" after the Real Madrid star was sent-off in the 1-1 LaLiga draw with Osasuna.
The England international was dismissed for dissent after just 39 minutes on Saturday following a heated exchange with referee Jose Munuera Montero.
Bellingham insisted it had been a "misunderstanding" and that he had not insulted the referee.
"It was disrespectful, it's not for me to decide (what exactly Bellingham meant) but I tell my players not to waste time or energy talking to the referees," said Flick on Sunday.
"Only the captain is supposed to talk to the referee and picking up a red card like that is bad for his team."
Real Madrid coach Carlo Ancelotti said Bellingham should not have been dismissed.
"I think with Bellingham's red card (the referee) didn't understand the English well... I don't think it's something offensive," Ancelotti told reporters.
It was Bellingham's second red card for Madrid since joining from Borussia Dortmund in 2023, with the first coming last March after arguing with referee Jesus Gil Manzano following a 2-2 draw at Valencia.
Barcelona can draw level on points with Madrid at the top of the table on Monday when they host Rayo Vallecano.