The English FA has opened an investigation into Chelsea's claim that a referee used "inappropriate language" toward its players during Sunday's 3-2 loss to Manchester United.
Chelsea accused referee Mark Clattenburg of insulting two players and lodged an official complaint with the FA.
English football's governing body said Monday in a statement: "The FA has begun an investigation relating to allegations made following Sunday's fixture."
Clattenburg sent off two Chelsea players in Sunday's 3-2 loss to United at Stamford Bridge and allowed a contentious late winning goal to striker Javier Hernandez, who appeared to be offside when he scored.
Clattenburg is one of the FIFA candidates to referee at the 2014 World Cup in Brazil.