When Louis van Gaal took over the reigns of the Old Trafford hot seat this summer the Dutchman was immediately presented with the challenge of having to rebuild and strengthen a squad capable of challenging for a record 21st league title.
With the club entering a new era, coupled with the departures of veteran defenders Patrice Evra, Rio Ferdinand and Nemanja Vidic, United's defence is understandably an area of concern for most fans associated with the club.
At current the Red Devils only possess three recognised centre-backs in Jonny Evans, Phil Jones and Chris Smalling. Though all three have endured injury prone periods in recent seasons, with Evans missing the majority of last season through injury himself.
During Sir Alex Ferguson's reign both Jones and Smalling were used sparingly. Often operating at right-back or in central midfield in Jones' case. With both failing to nail down a regular berth at centre-back, usually due to the presence of both Ferdinand and Vidic.
However all three impressed during pre-season with Jones and Smalling in particular forming a strong partnership in Van Gaal's new 3-5-2 formation. The Dutchman himself has said he will only buy once he has had a chance to look over and judge the current squad. Although following United's first opening home league defeat since 1972 against Swansea, it would now seem inevitable that defensive reinforcements will arrive before the close of the transfer window.
One name that was consistently linked to United throughout the window was that of Arsenal's Thomas Vermaelen. Following a disappointing season for the Gunners, the Belgian was deemed surplus to requirements at the Emirates, with Old Trafford seeming the likeliest destination. However the defender instead opted to join Spanish giants FC Barcelona for a fee of £15 million, forcing the Reds to pursue other options.
Borussia Dortmund's Mats Hummels has also seen his stock rise recently after being at the pinnacle of a German defence that went on to win the 2014 World Cup. The German has been linked to United on a number of occasions this summer. However coach Jurgen Klopp has reiterated his desire to retain the bulk of his current squad having seen star players Mario Gotze and Robert Lewandowski both depart the Signal Iduna Park in recent seasons.
Argentina's Marcos Rojo is also reportedly another target, with the defender requesting a transfer to the Red Devils from current club Sporting Lisbon according to Sky Sports News.
However they face stiff competition for his signature, with Southampton and Liverpool both reportedly readying bids for the South American. Sporting themselves are also thought to not be willing to do business, with the Portuguese club holding out for the release clause in his contract, which is believed to be €24 million.
During United's pre-season tour of the USA Van Gaal gave regular game time to academy graduates Michael Keane and Tyler Blackett, with the latter starting in the opening weekend defeat to Swansea. However it is highly unlikely that the Dutchman would use either on a regular basis as the season progresses.
Although both represent prospects for the future, neither have any real experience at Premier League level. It's far more likely that both will spend time out on loan this season.
Even though Van Gaal is renowned for his ability to develop young talent, it would be a risk beyond taking to continue the season with the current back line. With the Red Devils not competing in European football this season, the pressure is on for United to improve drastically on last seasons 7th place finish.
The Dutchman said after the opening week-end that he now 'knows' what areas he needs to improve, the question is can he bring in the personnel to help bring success back to the Theatre of Dreams.