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.