Leeds have vowed to hand lifetime bans to any fans found to have thrown missiles at Manchester United players after the FA confirmed they are investigating disorder at Sunday's match.
Anthony Elanga was struck by an object flung from the crowd while celebrating the Red Devils' third goal in their highly-charged 4-2 victory at Elland Road.
Leeds were reviewing CCTV footage to identify the offender on Monday and insist they will hand out the strongest possible sanctions to any guilty supporters.
West Yorkshire Police revealed they made nine arrests for a number of offences surrounding the Roses clash, including the throwing of missiles.