Real Madrid have opened an investigation into alleged racist abuse aimed at Barcelona teenager Lamine Yamal following their 4-0 defeat at the Santiago Bernabeu.Videos on social media appear to show the 17-year-old being subjected to taunts by a section of home fans as he celebrated his 77th-minute goal by pointing to his name on the back of his shirt.Robert Lewandowski scored twice and Raphinha completed the scoring as the visitors cruised to a win that takes them six points above their rivals at the top of LaLiga.A Real Madrid statement read: "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."Real Madrid has opened an investigation in order to locate and identify the perpetrators of these deplorable and despicable insults so that the appropriate disciplinary and judicial measures can be taken." Follow the RTÉ Sport WhatsApp channel for the best news, interviews, analysis and features, as well as details of our sports coverage across all RTÉ platforms.