The Football Association has announced an investigation into a complaint made by Chelsea that referee Mark Clattenburg used inappropriate language towards two of their players during their 3-2 defeat against Manchester United on Sunday.
Clattenburg - who was given the full backing of Prospect, the referees' union, on Monday morning - is thought to have made comments to Juan Mata and John Obi Mikel.
The comments are described as containing "inappropriate language" which was interpreted by the players in question as being racist.
The FA's statement read: "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 game at Stamford Bridge became heated during the second half, as Clattenburg dismissed two Chelsea players - Branislav Ivanovic and Fernando Torres - whilst the match was being tightly contested at 2-2.