This was only United’s second defeat in 18 games on their travels in the group stage and the first time they have failed to score in 20 European ties.
But with qualification for the knockout stage already assured for the men from Old Trafford boss Sir Alex Ferguson decided to give his younger players experience.
With the result scoreless at half-time the youngsters had acquitted themselves well in the intimidating atmosphere in Turkey, but all their good work was undone shortly after the restart.
Slack marking at a corner allowed striker Burak Yilmaz to score his fifth goal of the group stage with a header.
The hosts continued to create the better chances but even when United rallied they rarely troubled the Galatasaray rearguard.
Referee: Carlos Velasco Carballo (ESP)
Venue: Turk Telecom Arena
Galatasaray scorers: Yilmaz 54
Man Utd scorers:
Yellow cards: Rafael (MANU), Kaya (GAL), Yilmaz (GAL)