But they weren’t keeping tabs on Tottenham midfielder Eric Dier, who has been linked with a move to Old Trafford this summer.
Nor any of the Spurs man’s talented teammates who represent everyone from Chelsea and Arsenal to Manchester City and Liverpool.
Instead they were there to watch a young Scotland international take to the field.
Although Man United are looking to spend eye-watering sums of money when the transfer window opens next month, they are also in the market for a coup.
The man at the top of this list is Celtic left-back Kieran Tierney, who has also been linked with a possible move to Chelsea in recent weeks.
The 19-year-old has spoken out about the speculation linking him to the Premier League elite, telling Sky Sports he is “flattered” by the interest being shown him in.
He quickly followed this up by claiming he is very happy at Celtic however, and therefore not necessary looking to leave Parkhead.
But United are still keeping track of his progress, and according to the Daily Star,deployed a trio of scouts to watch him in action.
The teenager, who was handed his Bhoys debut by Ronny Deila, played the full 90 minutes of the World Cup qualifier, which finished in frenetic fashion.
He has impressed for Celtic this season, particularly in the Champions League, and would command a £17million price tag, according to reports.