CHELSEA last night lodged a formal complaint with the Football Association over ‘‘inappropriate language’’ they claim Mark Clattenburg used against John Obi Mikel in their acrimonious defeat to Manchester United on Sunday.

But the Blues decided not to pursue an allegation referee Clattenburg, originally from Consett, County Durham, also used words understood to have been interpreted as racist towards Juan Mata during Sunday’s game following an internal investigation carried out by external legal counsel.

It is understood Chelsea submitted signed witness statements from a number of players and staff to the FA, who had already begun their own probe into the matter.

The police are also investigating the allegations against Clattenburg, who it is understood categorically denies any wrongdoing.

Chelsea said in a statement: ‘‘Following Sunday’s Premier League game, club board members were quickly made aware, upon entering the home dressing room after the final whistle, that there were allegations of inappropriate language directed at Chelsea FC players by Mr Clattenburg during the game.

‘‘Board members began establishing the details of the allegations, speaking to all relevant players and staff. After those initial interviews, it was clear that the matter had to be reported.

‘‘The correct protocol for doing so was to report the incidents to the match delegate, and the club took immediate steps to inform him as soon as he was available. It was not a decision the club took lightly.

‘‘Since reporting the matter to the delegate, the club and outside legal counsel have conducted further investigations.

‘‘Having completed that process, we have now followed the correct protocol and lodged a formal complaint with the FA regarding John Mikel Obi.

‘‘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.

‘‘We will cooperate fully with the FA and the police as they each investigate the matter.

As events on Sunday are now subject to those investigations, we are unable to comment further.’’ The FA did not respond as they continued their probe.