A man has been arrested on suspicion of a "racially aggravated public order" during Saturday's clash between Manchester City and Manchester United, Greater Manchester Police has confirmed.
During the second half of United's 2-1 win at the Etihad Stadium, the visitor's midfielder Fred appeared to be hit by an object thrown from the crowd as he prepared to take a corner.
Lighters and a plastic bottle could be seen by the corner flag, while television footage seemed to show a supporter making racist gestures in the direction of Brazil international Fred and his team-mate Jesse Lingard.
Shortly after full-time, City released a statement saying it was investigating and threatened to issue life bans to any individual found to have committed racial abuse.
In a statement, Greater Manchester Police said: "A man has been arrested after a video posted on social media showed a supporter making racist gestures at the Manchester City v Manchester United match at the Etihad Stadium yesterday.
"At around 6.55pm on Saturday 7 December 2019 police were called to a report of a supporter making alleged racist gestures and sounds towards players during the Manchester City and Manchester United derby.
"A 41-year-old man has been arrested on suspicion of a racially aggravated public order and remains in custody for questioning."
Superintendent Chris Hill of the City of Manchester Division added: "I would like to thank the public for their ongoing support with this incident.
"Racism of any kind has no place in football or our society and 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 enquiries."