Chelsea have lodged an official complaint to the FA over allegations surrounding comments made by Mark Clattenburg to John Obi Mikel during Sunday's game against Manchester United, the club have confirmed.
A statement on the club's official website read: "Chelsea Football Club today lodged a formal complaint with The Football Association regarding inappropriate language directed at John Mikel Obi by referee Mark Clattenburg. This is a result of a thorough investigation carried out by the club, and led by outside legal counsel, of all information available to us including interviews with a number of players and staff."
Chelsea have already reporte the matter to the match delegate, as is standard procedure, but have now made their complaint formally to the FA. The club did, however, confirm that they will not be following up other allegations, saying: " There was not sufficient evidence to support a second claim to The FA with regard to the alleged verbal abuse of another first team player."
Clattenburg has had his side of the story heard by the referee's union, which has decided to back their man fully, so the case has the potential to be highly-charged.
Chelsea also confirmed that they "are unable to comment further until those processes are complete."