The Football Association is investigating after Manchester United's Anthony Elanga was struck by an object thrown from the crowd in Sunday's Premier League victory at Leeds United.
Elanga, 19, was hit by a missile as the visitors celebrated Fred's 70th-minute goal in the 4-2 win at Elland Road.
There were also numerous unsavoury chants from both sets of supporters.
It was the first game in front of fans between the two old rivals at Elland Road since October 2003.
Elanga scored his side's fourth goal with two minutes remaining to confirm victory for Ralf Rangnick's visitors, after Leeds had levelled from two goals down in a fiery encounter.