Wayne Rooney has shouldered much of the load for United this season.
Manchester United fans have been baffled by their poor form so far this season, after a squad that comfortably won them a title last year now has the club in seventh place in the Premier League.
Most rational supporters realized that their club had overachieved with Sir Alex Ferguson at the helm, but they at least expected David Moyes to produce a top-four finish.
That hasn't looked likely thus far.
While some of it can be attributed to Moyes' tactical inefficiencies and poor squad selection, United's struggles also boil down to a lack of squad depth.
Though they've come to be known as a perennial powerhouse with an abundance of world-class players, the Red Devils' current squad does not fit that description.
They have players like Wayne Rooney and Robin van Persie, who are absolutely elite; borderline world-class players like Michael Carrick, David de Gea, Rafael and Danny Welbeck; and players like Shinji Kagawa and Adnan Januzaj, who could earn this label in the future with a little more development and consistency.
Other than that, United's squad is made up of aging stars who are no longer themselves (Patrice Evra, Nemanja Vidic) and good, but not great players who lack the quality to be every-game starters (Jonny Evans, Tom Cleverley and Javier Hernandez).
He leads the team in goals and assists, with nine apiece, and has enjoyed a resurgent season amid United's struggles. Good form from Rooney alone, however, has not always been enough to earn United a result, so it isn't any surprise that they struggle mightily when he doesn't grace them with their presence.
United, without Rooney on the pitch, have lost successive matches to Swansea and Sunderland, looking uninspired and devoid of a true goalscorer or creator.
This, is where United have a real problem.
At full-strength, they can usually compete with any team in the league, but their reserves or non-stars are not good enough to earn those results on their own.
United suffer immensely when having to sub out a player like Rooney for a less talented one like Hernandez.
Meanwhile, the current top three can pick quality players right off their benches and seamlessly continue winning games.
Sergio Aguero needs to rest a game? Alvaro Negredo will be a more-than-adequate replacement (eight goals).
Jack Wilshere was suspended two games for flipping off Manchester City fans? Take your pick from Mikel Arteta, Aaron Ramsey or Mathieu Flamini.
With bundles of elite talent rotating in and out, these clubs' players stay fresh, and one single player is never relied on to the extent that Rooney is at United.
Perhaps one of these clubs poses a more attractive option than United for the rest of his career, as his teammates wouldn't be relying on him for a miracle every match, and he could play with far less pressure.
Per ESPN UK, Rooney is currently mulling his contract situation at Old Trafford, as David Moyes admits he is not sure whether the striker will sign a new deal.
In this day and age, star athletes would rather be part of a great team than be the team themselves.
Gareth Bale recently joined Real Madrid from Spurs, Neymar preferred to move to Barcelona than to remain the star player at Santos and basketball player LeBron James chose to join the Miami Heat instead of staying to shoulder a much heavier load at the Cleveland Cavaliers.
For Rooney to sign a new deal, his supporting cast will have to lend him a lot more help, and Van Persie, Rafael, De Gea, Carrick and Welbeck will have to continue to be the quality players that they are.
Will Wayne Rooney still be at United by 2015?
David Moyes could try to bolster that supporting cast in the January transfer window, as he will be given a massive £200 million budget to rebuild the team, according to a report by Chris Wheeler in The Daily Mail.
However, if United fail to improve their squad in either of the upcoming transfer windows, it could become tough for them to re-sign Rooney, and it could be even tougher to return to the top of the table anytime soon.
Information from ESPNFC and Goal.com was used in this article.