1) Mats Hummels (Borussia Dortmund)
A truly world class centre-back, United could be set to spend around £30m on another Borussia Dortmund star in Mats Hummels. The German international has been a rock for club and country in recent years, and was strongly linked with the Red Devils over the summer. With United’s defence looking poor so far this season, Hummels might be the most important signing the club could make this January.