Chelsea announced Thursday they had launched an investigation after a supporter was photographed apparently making a racist gesture towards a black Manchester United player.
The picture, published in several British newspapers, was taken during Chelsea's dramatic 5-4 League Cup win over Manchester United at Stamford Bridge on Wednesday and appeared to show a fan making a monkey gesture at striker Danny Welbeck.
"Chelsea Football Club can confirm we are investigating an incident involving a member of the crowd at last night's game against Manchester United," the west London side said in a statement.
"The club will be examining all available footage and asks anyone who can identify the individual to contact the club.
"Chelsea FC is committed to removing all forms of discrimination and if we have sufficient evidence we will take the strongest possible action, including supporting criminal prosecution."
A similar complaint involving Spanish midfielder Juan Mata was dropped by the club.
But while London's Metropolitan Police are investigating Clattenburg's alleged comments to Mikel, they have not, as yet, inquired into the supporter's apparent gesture.
"We are aware of the picture but we have not received a complaint," a police spokesman said Thursday.
Chelsea captain John Terry is currently serving a four-match ban imposed by the FA for racially abusing Queens Park Rangers' Anton Ferdinand during a match in October last year.
Earlier this year Chelsea banned for life a supporter who admitted racially abusing former player Didier Drogba.