There were nasty scenes at the end of the game as United players celebrated a goal with their fans and Rio Ferdinand was hit just above the eye with a coin that left him with a face dripping with blood.
One idiot, 21 year old Matthew Stott tried to get at Ferdinand as he recovered from the incident, but the fan wearing the blue and white of City was restrained by goalkeeper Joe Hart.
"Despite fierce rivalry and high tension there was no major disorder," Greater Manchester Police chief inspector Steve Howard said in a statement.
"However, we will continue to investigate the coin throwing incident and are determined to work with the club to bring the perpetrator to justice."
Stott was one of two men charged with pitch encroachment, issued an apology through his solicitors on Monday, saying: "I would like to apologise to all those affected by my actions yesterday particularly Mr Ferdinand and the other players.
"I am extremely ashamed of my actions. I have let myself down, my family down, my fellow fans down and Manchester City Football club. I intend to write personally to Mr Ferdinand to express my extreme regret and apologies and also apologise to Manchester United and their fans.
"I would like to thank Joe Hart for his actions when I came on the pitch."