Current Club: Dortmund Arguably the biggest single question that Van Gaal faces at United this summer is how he fills the sizeable gap left by Nemanja Vidic, and the answer could well lie with an imposing centre-half who was linked to the club before Van Gaal came in: Dortmund's Mats Hummels. Any deal would likely be bolstered by the fact that the player, who has put in some imperious displays for the German side since becoming a first team regularly, has apparently expressed his desire to join the club - though that was supposedly on the proviso that the side would qualify for the Champions League. With a likely sizeable fee required to prize him away from Germany, Hummels would have to be an immediate solution to United's defensive problems, but he has proven in his seven years at Dortmund so far that he is more than capable of commanding a defence. And at 25 years old, United could potentially be looking at a ten year return on investment, and the kind of strong foundation stone they have lacked since Rio Ferdinand's pace and power began to wane.