Chelsea complaint about inappropriate language
On 28 October 2012, Chelsea made a formal complaint to the Football Association against Clattenburg about his alleged use of "inappropriate language" towards John Obi Mikel during that day's match against Manchester United. Due to a lack of evidence the club said it decided not to complain about alleged verbal abuse of a second player,.[43] United had won the game 3–2, scoring the winning goal after the referee had sent off Chelsea's Branislav Ivanović for a professional foul and then showed Fernando Torres two yellow cards, for a high kick and alleged diving. Replays showed that the winning goal should have been ruled offside.[44]

The Professional Game Match Officials Board stated that Clattenburg would fully co-operate with the FA's investigation into the complaint.[45][46] The PGMOB also announced that it would not appoint Clattenburg to referee a match the following weekend, stating that the "scrutiny [of Clattenburg] would detract from the match and be unfair to the clubs and the supporters of both sides."[47] Clattenburg was also not appointed to referee a game the subsequent three weekends.

On 30 October, the Metropolitan Police Service launched its own investigation into the allegations after it received a complaint from the Society of Black Lawyers. It was reported that Mikel did not hear Clattenburg's alleged racist remark, but was told about it by team-mate Ramires. It was alleged to have been made after the official booked Mikel in the 76th minute for dissent following the dismissal of Torres. After the game, some Chelsea staff and players, including Mikel, were alleged to have entered the referee's dressing room and a confrontation took place.[48]

The police investigation was dropped on 13 November.[49] The Metropolitan Police said in a statement: "[N]o victims have come forward. Without a victim and/or any evidence that any offence has been committed, the matter cannot currently be investigated."[50][51] The FA cleared Clattenburg of wrongdoing nine days later and charged Mikel with using "threatening and/or abusive and/or insulting words and/or behaviour" towards Clattenberg after the match.[52] Mikel was found guilty and received a three match ban and a £60,000 fine.[53]

Clattenburg said in a statement: "To know you were innocent of something but that there was the opportunity for it to wreck your career was truly frightening. I hope no referee has to go through this in the future. We are proud of the integrity of refereeing in this country and I cannot wait to be back involved in the game I care so passionately about".[54]

He returned to duty as the fourth official for a fixture between Tottenham Hotspur and West Ham United on 25 November and refereed Norwich City's Premier League game at Southampton for his full return to the middle on 28 November 2012.[55] He was given a standing ovation by sections of both sets of fans at the game, which finished 1-1, and the managers of both clubs said afterward that they were "pleased to see him back".[56]