Barcelona boss Hansi Flick has accused Jude Bellingham of being "disrespectful" after the England midfielder was sent off for Real Madrid on Saturday night.
Bellingham received the second red card of his Real career during their 1-1 LaLiga draw at Osasuna.
Referee Jose Luis Munuera Montero dismissed Bellingham in the 39th minute for dissent, although the 21-year-old insisted after the game that he was wrongly sent off.
Bellingham was quoted in the Spanish media as saying: "I do not want to go into the details of what was said, but I didn't insult the referee.
"I hope they review the footage because it was a misunderstanding, but I am here to apologise to the team as I put them in a difficult situation."
Real boss Ancelotti backed Bellingham at his post-match press conference on Saturday, saying: "I think the referee did not understand Jude Bellingham's English. He said f*** off, not f*** you... that's way different.
"I won't talk more about the referee as I want to be on the bench next week."
But Bellingham's actions were criticised by Flick ahead of Barcelona's home game against Rayo Vallecano on Monday.
Asked about Bellingham's expulsion, Flick said: "It is disrespectful but I'm not the one who should comment on it.
"And that's what I've always told the players. Why waste time and energy arguing with the referee regarding the decisions he makes?
"There is a player, who is the captain, who has the right to argue with the referee.
"I don't like the behaviour I saw yesterday and I told the players that today. It's a weakness when you get a red card."
Barcelona will move level on points with leaders Real if they beat sixth-placed Rayo.
