Ferdinand appeared to be hit by a coin as he celebrated his side's third goal in their 3-2 victory at the Etihad Stadium.
After Ferdinand was struck by the object, a Manchester City fan ran onto the pitch in the England defender's direction.
He slipped and fell to the ground as he approached Ferdinand but was then obstructed by City goalkeeper Joe Hart who pushed him away.
Ferdinand tweeted: "Respect to Joe Hart for protecting that idiot who ran on!! Love the banter between fans but there is a point when it goes too far...calm it!"