Prior to this season, Rooney was one of the Red Devils' most important players. That all changed upon the arrival of Robin van Persie.
Many were skeptical of the Dutch striker moving to Old Trafford. Sure he's a world-class striker, but United already had plenty of options in the attack. The logic was that the club could be improved in other ways.
Instead, Van Persie has become arguably the most important player in the Premier League.
In addition, United have shown that they can be successful even without Rooney at this stage.
The club reported on its website earlier in the week that Rooney's recovery from a knee gash wasn't on schedule, an as a result, he would miss the FA Cup game against West Ham and will not play this weekend against Liverpool.
However, as the Daily Mirror has pointed out, Rooney could very well make an appearance at the FA Cup replay next weekend.
Upon his return to full health, Rooney will be an almost automatic inclusion in the squad. Some might think that the striker can push United even further ahead of Manchester City in the Premier League table and get the club closer to a European title.
Really, though, does Rooney make United all that much better than they are right now?
Van Persie brings to United all of the great assets that a club looks for in a striker. In addition, he is the kind of player that Rooney has failed to become.
Rooney is a world-class striker, and he's won numerous Player of the Year awards. He hasn't, however, been the kind of talisman that United has been looking for.
When he's at his best, Rooney can turn a game around and single-handedly get the Red Devils a win. That hasn't happened enough, though.
He's one of the most frustrating players in the Premier League because when he's on form, he's great. On the other hand, when Rooney struggles, it's very glaring.
Van Persie has shown over the past few seasons that he is that kind of player. He did it at Arsenal, and he's doing it right now with United.
In addition, Rooney can't help what have been the biggest problems with the club so far—midfield and defense.
The center of midfield hasn't been addressed at all over the last few years. Roy Keane has never really been replaced, and while defensive midfielders are being outmoded, United could still use a dependable ball-winner.
It's both incredible and confounding that Sir Alex Ferguson can consistently have Paul Scholes and Ryan Giggs together in midfield and be seven points atop the Premier League title.
And then there's the back four, which was a bedrock for the club during last year's league campaign.
United surrendered 33 goals in the Premier League all of last season. Just 21 games into this year, they have let in 29 goals.
Their defensive frailties were never more evident than in the 4-3 win against Newcastle.
Nemanja Vidic getting back to full health should help, but there's still problems at the back.
While United remain a flawed squad, they can get on just fine without Rooney.