Shortly after its controversial 3-2 defeat at home to Manchester United in the English Premier League on Sunday, Chelsea issued a formal complaint to the English FA accusing referee Mark Clattenburg of using “inappropriate language” towards two of its players, with club officials claiming that one of the instances involved racism.

The identities of the aggrieved players were not revealed, although the Guardian believes the pair to be Nigeria international John Obi Mikel and Spanish international Juan Mata; the former is understood to have visited Clattenburg in his room following the game. Other reports claim that Fernando Torres, whom Clattenburg presented with a second yellow card for diving, was the subject of the verbal abuse, not Mata.

The referees’ union, Professional Game Match Officials, which has now publicly backed Clattenburg, said he would comply fully with any investigation.

In a separate report, former referee Jeff Winter says that if convicted of racism, Clattenburg would be banned from officiating another match at any level for the rest of his life.