Ferdinand was celebrating Robin van Persie's stoppage time winner when he clutched his face and moved away with blood seeping from a wound near his eye.
The incident at City's Etihad Stadium detracted from a match full of raw passion and skill and United manager Alex Ferguson said a spate of recent crowd problems was becoming a cause for concern.
"It's unfortunate that a City fan runs on and coins are thrown," he told the BBC. "That shouldn't happen. The same thing happened at Chelsea, which was masked by all the other things. We could have done without that."
Referring to the incident at Stamford Bridge in October when a steward was injured by Chelsea fans when United celebrated an equally dramatic win, the Scot added: "At Chelsea, We had half a seat thrown on the pitch, coins, lighters, and nothing done about it. It's a problem."
A City spokesman said CCTV footage of the incident was being reviewed.
(Reporting by Martyn Herman, editing by Ed Osmond)