Leeds United's Robin Koch was left nursing a bloody injury after a nasty clash with Scott McTominay.
The pair were involved in a collision early on during the contest at Elland Road.
It left Koch on the ground after he was caught late by the Manchester United midfielder, although there appeared to be little malice in the coming together.
Blood was immediately visible on Koch's forehead and he went to ground to allow medical staff to rush on.
The German was able to be patched up and will wear a head band for the remainder of the game to stem the bleeding.
Concussion protocols have become increasingly influential in deciding whether players can continue after head knocks.
But Koch appeared to be more than capable of filling back in to his midfield role.
However the Leeds star then went down once more just before the half hour and gestured to suggest he was in some discomfort.
Koch was assisted off the pitch with Junior Firpo replacing him.
No more than a foul was given for the challenge despite the subsequent challenge from the Scottish midfielder.
The rivalry between Leeds and the Red Devils was always going to lead to a fiery encounter in Yorkshire.
It is the first time the two teams have squared off at Elland Road in front of fans for 18 years.
Former United captain Roy Keane said before the game: "The atmosphere is going to be electric. For Leeds fans, this is the game that they always look out for.
"I think the Man United players will be in for a treat today, in terms of the atmosphere. Some of them have never experienced it before."
He also added: "Leeds fans are pretty noisy but you should also enjoy that but you only enjoy that if you get a positive result. I think the way that Leeds will set up today no doubt will come and have a go at United."
