Manchester City have vowed zero-tolerance regarding discrimination after players said they were targeted during Saturday's derby at Etihad Stadium.
The club said they were aware of a video circulating on social media which appears to show a punter making monkey gestures toward Manchester United players.
The incident is reported to have happened when Frederico Rodrigues de Paula Santos (Fred) went to take a corner in the second half of the clash.
The 26-year-old Brazilian also appeared to be hit by an object thrown from the stands, with multiple Manchester United players since coming forward reporting similar abuse after the game.
The club have reported players' comments to referee Anthony Taylor.
"I wasn't aware of it during the game but it can happen and we've seen it happen lately. The fact it is still happening is not good enough." United forward Marcus Rashford said.
United manager Ole Gunnar Solskjaer slammed the video as "unacceptable".
"I've seen it on the video and the fella must be ashamed of himself," he said."... I hope he won't be watching any football any more."
Manchester City have since pledged to issue a lifetime ban to "anyone found guilty of racist abuse".
City will work with Greater Manchester Police to help identify the individuals involved.
Earlier this week, New Zealand Cricket (NZC) lodged a complaint with Tauranga police over similar racial abuse.
The abuse was directed at Jofra Archer near the end of the first Test against England at Bay Oval.
Information gathered from an inquiry which included studying CCTV footage, listening to audio, interviewing bystanders and obtaining material on social media has been incorporated into the complaint.