(CNN) -- English football's battle to eradicate racism suffered another blow on Thursday as police launched an investigation into allegations that a Chelsea supporter made a racist gesture towards a Manchester United player.
A photo of the fan making a "monkey" action, which appeared to be targeted at United's Danny Welbeck during a League Cup match that Chelsea won 5-4, was published in a British newspaper Thursday
Chelsea has launched its own investigation into the matter and has already promised to assist the police in any way possible.
A statement from the Metropolitan Police read: "Today, Thursday, November 1, police have received a complaint regarding alleged racist behavior at Stamford Bridge last night, Wednesday, October 31.
"An investigation has been launched. There have been no arrests and enquiries continue."
The incident follows Chelsea's claim that a referee made racial comments to one of the club's players during Sunday's 3-2 home defeat by United -- a controversial match in which the Premier League-leading team had two men sent off.
On Wednesday, Chelsea confirmed it had lodged a formal complaint with the Football Association after alleging that official Mark Clattenburg had used "inappropriate language towards John Obi Mikel.
Now the club has stated that it will take "the strongest possible action" against the supporter involved in Wednesday's incident.
"Chelsea Football Club can confirm we are investigating an incident involving a member of the crowd at last night's game against Manchester United," a spokesman said.
"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."
Chelsea banned a supporter for life in March after finding them guilty of racially abusing the club's former striker Didier Drogba.
Club captain John Terry is currently serving a four-match domestic suspension after the FA found him guilty of racially abusing Queens Park Rangers defender Anton Ferdinand despite the former England international having been earlier cleared in court.