LONDON (AP) -Just as English football was slowly recovering from a divisive, year-long racism saga, the Premier League has been plunged into renewed controversy.
And, yet again, the accusation being leveled is linked to racism - a problem thought to have been largely eradicated from English football in the 1990s.
The new allegation appears unprecedented for the world's richest football league: Chelsea claims the referee used "inappropriate language" toward two players in the globally televised Premier League match against Manchester United on Sunday.
Midfielder John Obi Mikel is believed to be one of the players who Chelsea say was targeted by referee Mark Clattenburg, whose language has reportedly been interpreted as being racially offensive.
Clattenburg has been backed by referees' union, Prospect, which issued a statement that highlighted the wider struggle against racism.
"Prospect is committed to helping to eradicate racism in football and in society generally," Prospect national secretary Alan Leighton said. "In the context of that commitment, Prospect is offering full support to Mark Clattenburg in relation to the allegations made against him."
The program for Sunday's match included Chelsea captain John Terry using his column to dedicate the fixture to the Kick It Out anti-racism campaign and pledging commitment to "eradicating all forms of discrimination."
But Terry wasn't available for selection for Sunday's 3-2 loss to United. The defender is serving a four-match ban for racially abusing Queens Park Rangers rival Anton Ferdinand a year ago.
The case only concluded last month, and the bitter fallout caused deep fractures in the English game.
With Liverpool striker Luis Suarez having been banned for eight matches for also racially abusing an opponent last year, there were complaints about the leniency of Terry's punishment.
Some players, including Manchester United defender Rio Ferdinand, the brother of Anton, refused to back a Kick It Out campaign in protest last weekend.
But before Sunday's match, an uneasy truce seemed to be declared between the two factions in the case.
Rio Ferdinand shook hands with Chelsea defender Ashley Cole, who had staunchly backed Terry and was targeted by the United player on Twitter that led to a Football Association fine. Cole himself was later fined for criticizing the FA investigation that led to Terry's ban.
Now the FA disciplinary department is busy again with the Clattenburg case.
"The FA has begun an investigation relating to allegations made following Sunday's fixture," English football's governing body said in a statement.
Clattenburg was already the brunt of criticism on Sunday before the serious allegations emerged.
He sent off Chelsea players Bransilav Ivanovic and Fernando Torres and allowed a contentious late winning goal to striker Javier Hernandez, who appeared to be offside when he scored.
But for the next week at least, Clattenburg, who is one of the FIFA candidates to referee at the 2014 World Cup in Brazil, won't be officiating in England.
"Professional Game Match Officials believe that with any football match the focus should not be on the officials but on the players and the game itself," the Premier League said in a statement. "Mark Clattenburg is one of the elite referees in world football and, in these circumstances, the intense level of scrutiny would detract from the match and be unfair to the clubs and the supporters of both sides."
In Scotland in 2004, referee Stuart Dougal was fined 200 pounds ($321) for swearing at Rangers player Christian Nerlinger during a match against Partick Thistle.
Dougal now fears the Chelsea complaint could lead to officials being afraid to talk to players on the pitch.
"If clubs are going to go down the route that Chelsea have gone, referees might stop communicating altogether with the players and that is no good," Dougal said. "(Referees) might be frightened to talk just in case somebody twists something they say. If somebody says something in jest, when you see it on paper in black and white, sometimes it doesn't look good.
"It would be detrimental to the game if referees stopped talking to players because you need to chat to them, to encourage and coax them along. Referees might be refereeing under fear of being reported for saying a word out of place."
European champion Chelsea was also at the center of a police investigation on Monday after a crowd surge during the United match led to a steward being crushed and requiring treatment at a hospital for an injured knee.
Chelsea fans rushed forward after Hernandez's disputed winner for United.
"We will look into it with the club. There should be CCTV," Metropolitan Police commissioner Bernard Hogan-Howe said. "Obviously, there was some dispute at the end of the game, given it had been quite a controversial game. What we have to find out is if there was just one person involved or if there were any more."
Rob Harris can be reached at http://twitter.com/RobHarris