FA will to take no action against Man City and Man United post-derby fracas
The visitors' celebrations after the December 10 contest are alleged to have sparked a row involving several players and staff from both teams in the corridor outside the dressing rooms.
During that altercation, it is understood that milk and water were thrown at United boss Jose Mourinho from within the City dressing room.
But in a statement, the Football Association said: "Following a review of the evidence provided by the clubs and independent eyewitnesses, the FA will be taking no formal action."