Paddy McNair was subbed off after just 39 minutes of the game with Southampton.
Manchester United have had to rely on plenty of young players this season, with one in particular making a massive jump up the ranks.
Northern Irishman Paddy McNair has been a regular member of the first-team this season after plenty of injuries afflicted the United defence throughout the campaign.
In that time he has proven himself to be an able defender. He has great positioning, is strong in the tackle and has a very good footballing brain. Up until now he has proven himself worthy of a place in the United set-up.
That was until Monday night, when he put in a poor performance against Southampton.
He was playing well initially in a two man central defensive partnership but struggled when Louis Van Gaal had to change for a three man defensive line-up.
He then struggled and was therefore hauled off in the 39th minute, with no injury to blame for his substitution, Ander Herrera replacing him.
For a 19-year-old it must have been a very hard pill to swallow, but he has a manager not afraid to make such big calls so early in the game.
One man who is backing him however is John O'Neill. Himself a former Northern Ireland international who played over 300 games for Leicester City, he has been speaking to the Belfast Telegraph about McNair's Southampton nightmare this week:
"I sympathise with Paddy... It is very embarrassing when it happens, obviously in front of the spectators who are there and the audience on TV. Paddy wasn't having the best of games."
"The lad is only 19, yet he is playing for Manchester United, one of the biggest clubs in the world. He's got to remain confident in his own ability, he's there on merit and you're not going to play brilliantly in every game.
"He's had one poor game, but that's what happens when you are with Manchester United. Everything gets blown out of proportion. The fact that he is playing there at 19, he'll overcome this.
"I just keep my fingers crossed that somewhere down the line we'll have McNair and Jonny Evans as the two centre-halves for Manchester United."
If McNair cannot get past this setback however he will join a long list of players to have never quite made the grade at Manchester United.