Referee Ramon Abatti crossed his forearms in front of his chest, which signals the activation of the anti-racism protocol, five minutes into stoppage time after a brief scuffle erupted following a foul on Germany international Ruediger.

Asked if Ruediger had been the victim of racism during the game, Alonso told a press conference: “That’s what Ruediger said, and we believe him.

“It is important to have zero tolerance in these kinds of situations. Fifa now is investigating. That’s all I can say.”

It was not immediately clear whether the alleged abuse came from the crowd or an opponent.

Football’s governing body Fifa was not immediately in a position to clarify the incident when contacted by Reuters, as it still awaits the referee’s report.

Ruediger, 32, has been the target of racist abuse several times when playing for Chelsea, both on the pitch and online, AS Roma and Real Madrid.