A man has been arrested after objects and racist abuse appeared to be targeted at Manchester United players during Saturday’s derby.
Police said they received a report of a fan making alleged racist gestures in the game against Manchester City.
City said they were working with police “regarding an instance of objects being thrown on to the field of play”.
A 41-year-old man has been held on suspicion of a racially aggravated public order and remains in custody.
On Saturday, a man was filmed apparently making monkey gestures and sounds towards Manchester United players during the derby at City’s Etihad Stadium.
It 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, the 26-year-old Brazilian 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.”
The FA said it would investigate the claims, and plans to speak to the clubs, referee Anthony Taylor and the police.
Supt Chris Hill, from GMP, 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 Stamford Bridge, 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 incidents on Saturday showed “we are still in a backward society”.
United won the match 2-1 after goals from Marcus Rashford and Anthony Martial.