I think the youngsters will do well, and it is important that they get their chances. I believr Alex Ferguson's mind is on Tuesday's Champions League game with Arsenal, they must get through to the finals. Comparatively, the Boro game is less of an importance as mathematically, Man Utd can afford to lose another game before the Premier League slips out of their grasp.
Having said that, I wouldn't expect Man Utd to lose this game, it's either a draw or they snatch the winner. If they can win this game, the title is practically in Old Trafford.