Manchester United midfielder Fred appeared to be struck by a flying missile from the Etihad Stadium crowd during Saturday night's Manchester derby.
The Brazilian was going over to take a corner when the object hit him in the back of the head. Manchester City midfielder, and fellow countryman, Fernandinho appeared to instruct his own fans to stop as Fred went down in pain after the incident.
United were leading 2-0 in at the 67-minute mark when Fred went over to take a United corner.
Goals from Marcus Rashford and Anthony Martial secured the lead for the visitors, against most fans' expectations, although Nicolas Otamendi hit back with a header to make it 2-1.
The Premier League and Manchester City are likely to release more information on the incident.
FA laws stipulate that "[if] an object thrown by a spectator hits a match official, a player or team official, the referee may allow the match to continue, or stop, suspend or abandon it depending on the severity of the incident."
Referee Anthony Taylor briefly paused the match before allowing it to continue.
A City statement said: "The Club are working with GMP regarding an instance of objects being thrown onto the field of play."
on an incident of alleged racial abuse towards United players during the game.
