Real Madrid condemned racism from some of their supporters aimed at Barcelona players including teenager Lamine Yamal and Alejandro Balde during the club's 4-0 Clasico defeat on Saturday.
"Real Madrid strongly condemns any kind of behaviour involving racism, xenophobia or violence in football and sport, and deeply regrets the insults that a few fans uttered last night in one of the corners of the stadium," said Los Blancos in a statement Sunday.
Videos emerged on social media after the game of racial abuse aimed at Barcelona players.
The Spanish champions said they had "opened an investigation in order to locate and identify the perpetrators of these deplorable and despicable insults".
Spanish football is struggling to combat racism in stadiums across the country.
Real Madrid striker Vinicius Junior has become a figurehead in the fight against racism and has been targeted on numerous occasions since arriving in Spain in 2018.
The Brazilian winger earned worldwide support in May 2023 when he squared off with Valencia supporters after suffering abuse at their Mestalla stadium.
In January 2023, an effigy in a Vinicius shirt was found hanging from a bridge near the club's training ground alongside a banner saying: "Madrid hates Real".
In December, four Atletico Madrid fans were charged over the incident, with prosecutors pushing for jail terms of four years.
This week Spanish police arrested four men suspected of inciting an online hate campaign against Vinicius.