An investigation has been launched by the Football Association (FA) after Manchester United prospect Anthony Elanga was struck by an object thrown from the Elland Road stands.
Backing up their midweek victory over Brighton, the Old Trafford giants earned cross-county bragging rights from their Premier League showdown with Leeds United on Sunday afternoon.
Goals from Harry Maguire, Bruno Fernandes, Fred and Elanga settled the scores in a 4-2 verdict.
However, there was an alarming flashpoint after substitute Fred netted in west Yorkshire.
United went over to the corner flag to celebrate restoring their lead and it was there where Elanga was struck on the head with an unconfirmed object thrown from the crowd.
The 19-year-old needed minor treatment as a result, but was deemed okay to continue.
The Academy graduate had the final say when he scored late on for United to rubber-stamp a memorable victory in what was the first meeting between these bitter rivals in front of supporters in the Premier League at Elland Road since 2003.
An unsavoury, if isolated, incident, match-goers had been warned about their behaviour by Leeds chief executive Angus Kinnear before the game. The FA are now set to look into the events that unfolded.
Writing in his programme notes, he said: "While the hostility of Elland Road is a definite competitive advantage we would all encourage, let's not mistake it for unsavoury and illegal behaviour that could mar our reputation - and it is not befitting of our club or city."
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