A man has been arrested after a fan was seen apparently making monkey gestures towards Manchester United players during Saturday’s derby.
Police said they received reports of a supporter making alleged racist gestures and sounds during the match against Manchester City.
A 41-year-old man has been held on suspicion of a racially aggravated public order and remains in custody.
The FA plans to speak to the clubs, referee Anthony Taylor and the police.
The incident happened as United midfielder Fred went to take a corner in the second half and appeared to be hit by an object hurled from the crowd.
After the match, Fred said: “On the field, I didn’t see anything. I saw it only in the locker room afterwards. The guys showed me. [A man] even threw a lighter and it hit me.”
United boss Ole Gunnar Solskjaer said: “Fred and Jesse [Lingard] were in the corner, taking a corner, and I’ve seen the video, heard from the boys.”
He said the apparent behaviour of the supporter caught on camera was “unacceptable”.
In a statement, Manchester City said they were working with police to identify offenders, adding: “The club are also working with GMP regarding an instance of objects being thrown on to the field of play.
“The club operates a zero-tolerance policy regarding discrimination of any kind, and anyone found guilty of racial abuse will be banned from the club for life.”
Supt Chris Hill said: “I hope this arrest shows that we are taking this matter extremely seriously.
“We will continue to work with Manchester City and Manchester United Football clubs on this incident and will investigate any other lines of inquiries.”
The incident comes a year after racism in football hit the headlines after City striker Raheem Sterling was subjected to racist abuse at c which led to a permanent ban for a Chelsea supporter.
Sterling was also one of a number of England players who faced monkey chants and Nazi salutes in Euro 2020 qualifiers this year.
Fred said the alleged incident on Saturday showed “we are still in a backward society”.