Louis van Gaal's team have endured a difficult festive season, with United winning just one of five league matches—a run which has seen the club drop out of third place and allow both Arsenal and Liverpool to make up ground in the race for Champions League qualification.
It is no coincidence that this difficult run has coincided with the absence of record signing Angel Di Maria, with the Argentinian missing the entire festive season due to a pelvic injury, as detailed by ESPNFC.
Di Maria has been one of the main positives of United's campaign so far, bringing a degree of speed and direct creativity from midfield, something United have lacked for a number of years.
In the 26-year-old's absence, Van Gaal's team struggled to form cohesive attacks starting from the back, and the former Madrid man's presence was missed just behind the forward line.
Since his move to United, Di Maria has been at his best when he receives the ball in a deep midfield position and then produces a 15- to 20-yard sprint with the ball before creating a chance for either himself or United's forward line.
With United utilising the 4-4-2 diamond system earlier in the season, most of United's attacking moves were started by a surging run from Di Maria. Not only did this put pressure on opposing defences, but it also allowed the likes of Robin van Persie and Radamel Falcao to operate solely in areas of great threat to the opposition goal—the pair enjoying the luxury of not having to drop into a deeper position in midfield to receive possession.
With Di Maria unavailable for selection, there isn't really anyone in United's squad who can contribute in the same manner. As a result, without him there has been a significantly larger gap between United's defence and attack than earlier in the season.
This has caused United's football to become laboured and stretched in recent weeks, with Jonny Evans being forced to play passes over slightly longer distances than usual, looking for either Van Persie or Falcao.
The forwards now have to drop deeper to receive the ball and thus are no longer in prime positions to score, hence United have found creating chances so difficult over recent weeks, particularly against Stoke City.
Sunday's loss to Southampton marked Di Maria's return to the first team, but unfortunately due to the situation surrounding Falcao being dropped by Van Gaal, as told by David Anderson of the Mirror, Di Maria found himself positioned as a centre-forward.
As hard as he worked, the position was not one where Di Maria could excel. There were very few opportunities where he could unleash his speed when in possession. Given how close he was to the Southampton penalty area, there was little room for him to kickstart a 15- to 20-yard forward run. Again, United found attacking strenuous and couldn't muster up a single shot on target.
Voted in the 2014 FIFPro World XI earlier this week, it is clear to everybody just how gifted Di Maria is. He is, by a clear distance, United's most important outfield player, and Van Gaal must begin to use him as such once more.
In truth, there have been restrictions placed on the Dutchman recently given the amount of injuries he has had to deal with, not least those which have afflicted Marouane Fellaini, Ander Herrera and Daley Blind. However, with all three now back to fitness, it is the time to revert back to either the 4-4-2 diamond system or the 4-5-1 with which United impressed just prior to Christmas.
While Di Maria is integral to United's play in an attacking sense, there must also be some consideration toward United's problems at the back. The issue with the 4-4-2 diamond and the reason why it was scrapped mid-season was it offered very little protection to the defensive four. With a confident, high-quality defence this may not be a problem. However, with United struggling for confidence at the back, it was a disaster.
The January transfer window is open, and according to ESPN's Miguel Delaney, the club are determined to try and recruit a central defender this month. This could have a significant impact on United's use of Di Maria, given that an experienced, confident head in a back four could give United the perfect platform to attack with freedom.
The United manager has instructed the club to spare no effort in trying to bring in Roma's Kevin Strootman this January rather than in the summer, sources said, while he also surveys a relatively lengthy list of centre-half targets.
United's A-list targets in that area are Mats Hummels and Diego Godin, but both are seen as highly unlikely.
United are also monitoring Aymeric Laporte of Athletic Bilbao.
With the race for Champions League qualification significantly closer than it was before Christmas, there is a real need for United to string together another run of victories. The club has the best possible chance of doing that if Di Maria is in good form and is used in the right way.
There is still a lot of time left in the transfer window for Van Gaal to take the necessary steps to facilitate such a change in team balance, a move that could take the shackles off Di Maria completely.
Given the Argentinian's comments to MUTV on Van Gaal's style earlier this week (h/t Carl Markham of the Daily Mail), it appears clear that the club's record signing is willing to do whatever it takes to drag United forward.