Man Utd are fighting for trophies, not fourth spot. The days off Man Utd vs Arsenal compeating for trophies are long gone.
Samir Nasri would be my first choice central midfielder to come in. Great little player with skill and pace and has an eye for goal, I think he'd link up well with both Wayne and Javier. Luka Modric wouldn't be a bad choice either but in my opinion, Samir is better. Might as well forget about Wesley Sneijder, would cost far to much money. Romours keep arising about Steven Defour. I haven't seen a lot off him in truth so can't really judge him.
Last season wasn't that long ago...