London - The English Football Association (FA) has launched an investigation into an official complaint from Chelsea after the club accused referee Mark Clattenburg of verbally abusing two of their players in Sunday's defeat by Manchester United.
"The FA has begun an investigation relating to allegations made following Sunday's fixture at Stamford Bridge between Chelsea and Manchester United," it said on its website (www.thefa.com) on Monday.
The affair is likely to plunge English soccer, which is only just recovering from one damaging crisis surrounding Chelsea, straight back into a new one involving the European champions.
Chelsea host United again in Wednesday's League Cup fourth-round match and although teams often rest leading players in the competition, the clash may take on extra significance given the controversy surrounding Sunday's Premier League encounter.
Chelsea said Clattenburg, who sent off two home players - Branislav Ivanovic and Fernando Torres - in the highly-charged 3-2 Stamford Bridge defeat, used "inappropriate language" towards two players.
The club would not name the players in question or of what nature the remarks were, but a spokesperson refused to deny that Nigerian midfielder John Obi Mikel had visited the referee's room after the game.
Mikel was booked for dissent during the second half.
Chelsea's decision to lodge a complaint against the FIFA-listed referee is largely unprecedented.
The club spokesperson told reporters: "We have lodged a complaint to the Premier League match delegate with regards to inappropriate language used by the referee and directed at two of our players in two separate incidents.
"The match delegate will pass the complaint to the Football Association. We will make no further comment at this time."
Clattenburg not only sent off two players but the officials rubbed salt into Chelsea's wounds by allowing Javier Hernandez's 75th minute goal that swung the outcome United's way to stand, even though he was marginally offside before scoring.
The referee has yet to comment but the Professional Game Match Officials Board (PGMO), which manages top English referees, said in a statement that Chelsea's allegations were "being treated with the utmost seriousness".
Clattenburg will co-operate fully and "welcomes the opportunity for the facts to be established," it added.
A number of Monday's British newspapers simply had the headline "Accused" on their back pages as featured in The Independent, Daily Mirror and Daily Express.
The Guardian had a banner headline "Ref in Chelsea race row" while the Daily Mail proclaimed "Ref Race Row" although those allegations have not been substantiated.
Chelsea are currently without skipper John Terry, who has served two games of a four-match domestic ban for racially abusing Queens Park Rangers defender Anton Ferdinand last year.
That case has blighted English soccer for a year after the former England player was also ordered to appear in court accused of a racially aggravated public order offence, of which he was acquitted.
The FA, however, using different standards of proof to guide its charge, found him guilty and fined him £220 000 as well as banning him. Terry waivered his right of appeal earlier this month.
Clattenburg, no stranger to controversy, was criticised by Chelsea manager Roberto Di Matteo for "ruining" the match.
While Ivanovic could have few complaints after accidentally impeding Ashley Young when the winger was through on goal, the decision to show Torres a second yellow for diving sparked outrage on and off the pitch as he appeared to be clipped.
"We must be disappointed that key decisions were wrong," Di Matteo told reporters.
"At 2-2, we looked like the team that was going to win the game. It was a good game between good teams and the official ruined it. Key decisions have to be right and you don't want the referees to have such a big influence.
"I think it's obvious in the eyes of everybody that the second yellow for Fernando was wrong. It was a foul for us and probably he should have booked their player.
"Their winning goal was an offside goal. It's a shame a game like that had to be decided by officials in that manner. Surely when he sees it, he will realise that he made big mistakes."
Torres's Spanish compatriot Juan Mata, who brought Chelsea back into the game at 2-1 with a stunning free kick, said Torres's dismissal was "incomprehensible".
"But I prefer to focus on the positives from the game - we competed against a great opponent and responded well to falling behind," he added.
Despite trailing 2-0 and clawing their way back to 2-2, Sunday's defeat was Chelsea's first in the Premier League this season but they remained top of the table on 22 points from their opening nine games - one point clear of Manchester United and champions Manchester City.