Willian has called for more action to be taken to eradicate racism in football after Chelsea team-mate Antonio Rudiger was allegedly abused during Sunday's 2-0 win at Tottenham.
Defender Rudiger was targeted shortly after Son Heung-min had been sent off for kicking out at his opponent during the second half of the Premier League fixture.
Chelsea captain Cesar Azpilicueta reported the incident to referee Anthony Taylor and an anti-racism message was relayed to supporters inside Tottenham Hotspur Stadium via the public address system.
Spurs' investigation into what happened "remains ongoing", the club confirmed on Tuesday, with Willian - who scored both goals in the London derby - hoping governing bodies will look to take a stronger stance on the issue.
"It's a shame. It's very disappointing, I don't know how people can think like that. In their team, they [Tottenham] have black players as well," the Brazil international told Sky Sports.
"I really don't understand what they think or why they do these kinds of things. I think we have to find, together, a way to stop this. It's a shame for everyone.
"Inside the pitch you cannot think much about this otherwise you are not concentrating [on your job]. We did all that we could do, our captain reports it to the referee that we had a manifestation of racism and the referee decides what to do.
"I hope we see more action from the federations, that's what we want."