Police say they are investigating after a 'string of racist abuse' was directed at a Manchester United player following the club's FA Cup fifth round match against Derby County.
CCTV images of four men police want to speak with have been released.
Derbyshire Constabulary said the alleged incident happened as United players were leaving Derby County's Pride Park stadium after the game on March 5.
The players were boarding the team bus at the time.
The force has confirmed the circulation of video footage online.
They said it 'captures the moment that a string of racist abuse is directed at one of the players'.
In a statement, Derbyshire Constabulary said: "Officers investigating an alleged incident of racist abuse at Pride Park Stadium following the FA Cup tie between Derby County FC and Manchester United FC have released images of four men they wish to speak to.
"As the Manchester United players were leaving the stadium a large number of fans were stood outside the team bus.
"Video footage that has circulated online captures the moment that a string of racist abuse is directed at one of the players.
"Officers conducting the enquiries are keen to speak to the people pictured who were in the area at the time the abuse occurred."
The force said the grainy images were the best available.
Both United and Derby County are said to have launched a joint investigation.
The two clubs are also thought to be aware of the footage in circulation.
The force hasn't identified the player involved.
Greater Manchester Police are said to be assisting the investigation.
Police constable Roger Brown, the dedicated officer for Derby County football policing, appealed for anyone with information to come forward.
He said: "Scenes such as this have no place in football.
"The match was fantastically supported by both home and away fans – unfortunately the actions of a mindless minority have cast a shadow over the tie.
"I, along with colleagues from both football clubs and colleagues from Greater Manchester Police, will work together to help bring those responsible to justice."
United ran out 3-0 winners against Wayne Rooney's new club.
Goals from Luke Shaw and a double from new striker Odion Ighalo set up a quarter final clash with Norwich City at Carrow Road on March 22.
