Barcelona said they would investigate alleged racist abuse of Vinicius Junior in their 2-1 Clasico defeat by Real Madrid on Saturday.
A video published by Spanish media outlets appeared to show a home supporter calling the Brazilian winger a "monkey", while an object that looks like a banana skin also appears to be thrown from elsewhere.
"FC Barcelona will always defend the values of football and sport such as respect for the opponent and we will investigate any racist insult that may have occurred this afternoon during the match against Real Madrid," said the Catalan club on X, formerly Twitter.
Vinicius, jeered by fans at Barcelona's temporary Olympic Stadium home throughout, particularly upset them when he was substituted late on after Jude Bellingham scored his second goal in stoppage time to win Madrid the game.
The 23-year-old walked off slowly, turning to the stands to celebrate, pumping his fists, with Madrid coach Carlo Ancelotti pulling him off the pitch by the arm.
"He came off very calmly, I told him he had to come off a bit quicker... I helped him off," said the Italian coach.
Vinicius also exchanged words with Xavi during the game over a challenge on him by Barcelona defender Ronald Araujo.
"I have a lot of respect for Vinicius, I told him it was not a foul," said Xavi.
Vinicius was also racially abused last Saturday in Madrid's draw at Sevilla, with one fan ejected.
The winger highlighted another video of a child appearing to make a racist gesture at him in the same match.
"Sorry to seem repetitive, but this is isolated episode number 19, and counting," said Vinicius in a statement last weekend.
He has been the victim of racist abuse on multiple other occasions during his time in Spain, although often no action has been taken by the law.
Vinicius testified before a Spanish court on October 5 by videoconference as part of an investigation into alleged abuse he suffered at Valencia in May.
The winger stopped the game at the Mestalla Stadium to face off with a fan he believed was abusing him, with Vinicius receiving global support for his actions.