The Metropolitan Police are investigating after Manchester United defender Victor Lindelof appeared to be struck by an object thrown from the crowd.
The incident happened as United's players celebrated after Bruno Fernandes made it 1-1 from the penalty spot.
A police statement said: "We are aware of an incident earlier at the #EmiratesFACup where an object was thrown towards the pitch during the first half of the game. We are working with officials at Wembley Stadium and reviewing CCTV footage."
