The official is alleged to have made an unsavoury remark during the Premier League game at Stamford Bridge, which United won 3-2 after the Blues were reduced to nine men.
A Chelsea statement read: “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.
“Following Sunday’s Premier League game against Manchester United, 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 until those processes are complete.”
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