Manchester United's defence hasn't exactly been water tight this season, with 43 goals conceded in the Premier League and 21 of those at Old Trafford meaning the Manchester clubs leaky defence let in more goals at home than any of the teams that finished in the top 5.
The departures of Namanja Vidic and Rio Ferdinand (and potentially Patrice Evra) compound United's need to sign at least one quality, experienced centre back and below, we'll be looking at the clubs potential defensive signings.
Mats Hummels (Borussia Dortmund)
Hummels would be a like-for-like replacement for Rio Ferdinand, good on the ball and can read the game exceptionally well. The German international would come with a price tag though and with clubs such as Barcelona interested United would have to offer a handsome wage packet to compensate for the lack of European football. Although big wages alone may not be enough to lure this Champions League finalist to Old Trafford.
Eliaquim Mangala (FC Porto)
Manchester City looked to be favourites to sign Mangala, who has a reported buy-out clause of around 50 million Euros. But with Financial Fair Play biting City in the backside recently they may be reluctant to splash that kind of cash on the Porto stalwart, giving United the edge if they went in for the player.
Ezequiel Garay (Benfica)
Garay is a name Manchester United fans will know all to well, as the Benfica and former Real Madrid defender has been linked with a move to Old Trafford since the beginning of time (almost). Apart from astute defending and a goal scoring knack Garay would bring a wealth of experience to the Red Devils back line.
Mehdi Benatia (AS Roma)
Benatia is another defender who can read the game brilliantly well and has Ferdinand-esque distribution. The Roma centre back reportedly turned down the chance of joining Jose Mourinho during the managers first stint at Chelsea and was also on David Moyes potential transfer list.
Federico Fazio (Sevilla)
More of unknown to Premier League and United fans, Fazio was linked with a move to Old Trafford shortly after the January transfer windows closed. The 27-year-old has helped guide Sevilla to the Europa League final and would certainly be a good buy, with the bonus of no premium price tag.