Chelsea have condemned the actions of a fan who was seen on social media aiming sectarian abuse at Aston Villa's Scottish international John McGinn.
Chelsea owner Roman Abramovich launched a major anti-racism campaign last year called No To Hate.
"We are aware of a video circulating on social media showing an individual using abusive language of a sectarian nature in the crowd at Stamford Bridge on Saturday," Chelsea said.
"Chelsea Football Club finds all forms of discriminatory behaviour totally unacceptable and we condemn the language used.
"The club is working to identify the person involved and will take the strongest possible action against them.