Gianni Infantino said he was "shocked" and "saddened" by the incident involving Gianluca Prestianni and Vinícius Júnior, stressing that "there is absolutely no room for racism" in football or in society.
In the same statement, the FIFA president praised referee François Letexier for activating the anti-racism protocol.
Infantino's full statement
"I was shocked and saddened to witness the alleged racist incident against Vinícius Júnior during the UEFA Champions League match between SL Benfica and Real Madrid FC.
"There is absolutely no place for racism in our sport or in society - we need all relevant stakeholders to take action and hold those responsible accountable.
"At FIFA, through the Global Initiative Against Racism and the Player Voice Panel, we are committed to ensuring that players, officials, and fans are respected and protected, and that appropriate measures are taken whenever incidents occur. I commend referee François Letexier for activating the anti-racism protocol by using the arm gesture to stop the match and manage the situation.
"FIFA and football stand in full solidarity with victims of racism and all forms of discrimination. I will always continue to repeat: No to racism! No to any form of discrimination!"