There's a scenario whereby they miss out on top 4 altogether. Chelsea beat them and win their other two games in hand and they're level on points (but well behind on GD). But if Liverpool drop points against Brighton in their last game and Chelsea beat Newcastle then Liverpool will finish fifth if Spurs win both their games in hand.
United could also miss out on top 4 mathematically - which would you prefer?
I would normally say pile as much misery on the rags as possible whenever possible, but after the last 2 weeks....