Chelsea have made a formal complaint against Clattenburg, accusing him of using “inappropriate language” towards two of their players on Sunday.
It is claimed Clattenburg used a racial slur towards a Chelsea player, believed to be midfielder John Mikel Obi is involved in the complaint.
The FA issued a statement on Monday saying:
The FA has begun an investigation relating to allegations made following Sunday’s fixture at Stamford Bridge between Chelsea and Manchester United (Sunday 28 October 2012).
The FA will make no further comment at this time.
The referees’ organisation Professional Game Match Officials (PGMO) issued a statement on Sunday night confirming Clattenburg would co-operate with any investigation.
“PGMO is aware of the allegations and they are being treated with the utmost seriousness,” the statement read.
“Mark will co-operate fully and welcomes the opportunity for the facts to be established.”
Unlike the Suarez and Terry racial abuse cases, this one should be easier to solve as assistant referees Michael McDonough and Simon Long and fourth official Michael Jones will have heard conversations between Clattenburg and the players as all four officials wear microphones and ear pieces that allow them to hear what each other is saying during the game. Unfortunately though, these conversations are not recorded.
“A referee’s microphone is on open. Everything he says is heard by two assistants,” Poll told BBC Radio 5 live.
“So if Mark said something, the assistants would have heard it.”
If found guilty, this has to be the end of Clatterburg’s refereeing career. If found innocent, what does it say about Chelsea, a club whose name has been tarnished by the recent John Terry racial abuse affair.