- Chelsea lodge official complaint with Football Association
- Mark Clattenburg accused of using "inappropriate language" towards John Obi Mikel
- Club will not pursue allegations of abuse towards Juan Mata by the referee
- Mark Clattenburg denies all allegations leveled at him
Chelsea has lodged a formal complaint with the Football Association after alleging referee Mark Clattenburg used "inappropriate language" towards John Obi Mikel during their Premier League defeat by Manchester United.
The European champions also stated that there is insufficient evidence to support allegations that Clattenburg abused Spain star Juan Mata.
The FA has already announced that it has launched an investigation into the incident, while the Metropolitan Police revealed on Tuesday that it will also conduct a probe.
The referee has refuted all allegations made against him, but that has not stopped Chelsea from taking its case further.
A statement on the official club 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.
"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."
Meanwhile, Mikel played 45 minutes as Chelsea defeated Manchester United 5-4 in a thrilling Capital One Cup encounter.
Ryan Giggs gave United a 22nd minute lead before David Luiz equalized from the penalty spot to bring Chelsea level.
Javier Hernandez put the visitors back in front, his sixth goal in nine games against Chelsea, before Gary Cahill headed home a second equalizer.
United grabbed the advantage for the third time just before the hour mark when Nani rounded off a flowing move only for Eden Hazard's 90th minute penalty to send the game into extra-time.
Daniel Sturridge then gave Chelsea the lead for the first time in the contest on 97 minutes and Ramires made sure of the victory added a fifth late on.
Giggs netted a penalty to make it a nervy last couple of minutes but Chelsea held out to book a quarterfinal place against Leeds United.
Elsewhere, Tottenham suffered a 2-1 loss at Norwich after Clint Dempsey failed to score a last minute penalty.
Cup holder Liverpool was also beaten, going down 3-1 to Swansea.