Visiting attackers Bryan Mbeumo and Sergi Canós appeared to be struck by objects from the crowd after they had combined to give the Bees a 2-1 lead.
Canós fell to the floor following his celebration in front of the Don Revie stand but was back on his feet quickly enough before being substituted later in the game.
The FA are now investigating the incident which is a violation of the governing body's rule E20.2.
The rule states that: “Each Affiliated Association, Competition and Club shall be responsible for ensuring that no spectators or unauthorised persons are permitted to encroach onto the pitch area, save for reasons of crowd safety, or to throw missiles, bottles or other potentially harmful or dangerous objects at or on to the pitch.”
The FA handbook also states: “The FA investigates almost all crowd management issues at fixtures.
“The FA’s investigations usually involve seeking observations from the club/s concerned and agencies such as the Police.
“The FA works closely with the club/s and any agencies to ensure that those responsible are identified, dealt with appropriately by the club/s and the criminal courts where appropriate."
Leeds had led at Elland Road through Tyler Roberts's opener but were behind early in the second half after Shandon Baptiste and Canos both found the net.
Patrick Bamford, on his return from injury, struck late on to rescue a point for Marcelo Bielsa's side.