The Red Devils were without several of their star players, but even still, Sir Alex Ferguson's men were expected to cruise to victory over a Norwich City side that has failed to produce anything other than attacking inconsistencies this season.
However, it would be United who would fail to capitalize on their attacking opportunities and surrender three possible competition points in the process.
Here's six things we learned from the shocking loss this weekend.
With the arrival of Robin van Persie to United's attack this season, Wayne Rooney has to continue to harness his creative skills and his ability to act as the club's playmaker.
And it was Rooney's play-making ability that the Red Devils dearly missed against Norwich, with United unable to get anything going against the Canaries throughout midfield because the England international didn't play due to an ankle injury (per The Metro).
Interestingly, the flow-on effects from Rooney's absence were telling, with Michael Carrick and Ryan Giggs forced to spark the attack rather than just hold the side together—something that the pair struggled to do for the majority of the match.
It also forced Dutch international van Persie, whose goal-scoring has become synonymous with United's success this season, to drop further back downfield to help. This reduced some of the attacking edge that the 29-year-old brings to the side.
Throw in the obvious attacking and goal-scoring threat that Rooney brings to the table, and he was definitely the player that United missed the most this weekend.
The final scoreline proves it.
With Champions League fixtures looming this weekend, Sir Alex Ferguson opted for a more experienced central midfield pairing in Ryan Giggs and Michael Carrick against Norwich City—a move that backfired for the Red Devils' boss.
Neither player was strong against the Canaries' midfield—in attack or defense—and neither got the better of Alexander Tettey or Bradley Johnson, showing that age was not the answer for United here.
Paul Scholes wasn't introduced until the 69th minute by Ferguson. When he was introduced, he didn't even replace one of the struggling central midfielders. The same can be said for Anderson, who came on for Rio Ferdinand in the waning minutes of the game.
Tom Cleverley isn't the world's best central midfielder, but he has been United's best option in the middle this season. He should have been used by Fergie here.
In a game in which the Red Devils' average midfield age was over 32, maybe it is fair to say that some youth wouldn't have gone astray in this one.
Last season, Nemanja Vidic's season-ending injury was viewed by many as the moment where United's title aspirations began to unravel.
And whilst they are in a far stronger position this year than they were 12 months ago, it must be noted that injuries to key players are beginning to hurt the Red Devils.
On the defensive end, Phil Jones, Chris Smalling and Nemanja Vidic have all spent significant time on the sidelines due to injury. Captain Vidic is likely to be out until after Christmas, according to the latest report from The Telegraph.
In attack, it's been time out for Wayne Rooney and Shinji Kagawa that has most hurt the Red Devils, with their creativity lacking due to the duo's absence.
United's title hopes are definitely stronger than they were last year, and their squad is significantly stronger also. But when even the most innocuous injury can derail an entire season—like we've seen for the Manchester club before—it's definitely worth keeping an eye on that injury list at Old Trafford.
Let's move away from Manchester United here for a second and give Norwich City the proper credit that they deserve for beating the Red Devils fair and square.
They kept the most prolific attack in the Premier League to date scoreless and controlled the match throughout midfield—making this more than just a "lucky" 1-0 victory.
Truth be told, Carrow Road is becoming an increasingly difficult place to get a result in the Premier League this season. It could nearly be included with the likes of the Etihad and Britannia Stadium as the hardest road trips to make in the league.
Since being belted 5-2 by Liverpool at home over a month ago, Norwich have posted three consecutive victories at home—keeping their opponents scoreless in that time also. Not that their opponents were easy beats, with Arsenal, Stoke City and now Manchester United falling to the Canaries.
If you take out that five-goal drubbing, Norwich have only conceded one other goal at home this year. They haven't been beaten at Carrow Road, either.
Norwich really isn't an easy journey to make anymore.
Manchester United's Player of the Year last season, Antonio Valencia, is one of the most talented wingers in world football, but he dearly, dearly needs a left foot.
The Ecuadorian international is becoming somewhat of a "one trick pony" out on the right flank. Whilst he still possesses great ability and skill to beat a man one-on-one, the 27-year-old would no doubt be better served if he were able to move either side.
According to FourFourTwo's Stats Zone, Valencia completed 27 of his 31 passes attempted for the match, but only 11 of those passes were traveling in a forward direction. The remainder were either back passes to Rafael da Silva or inside balls—slowing down the Red Devils attack.
Several times, he failed to play in Rafael who had overlapped out wide, and it was down his side also that Norwich created the opportunity to net the only goal of the match.
Valencia is still a brilliant winger who has a future at Old Trafford as long as he would like. But seriously, get a left foot. It's starting to drive us all mad.
According to WhoScored, this was the first time all season that Manchester United had lined up in the typical 4-4-2 formation that has become so accustomed with the club.
And especially without their best creative midfielders at hand, the 4-4-2 simply wasn't the formation for United to choose—giving further credence to the midfield diamond formation that the Red Devils have had strong success with this season.
Ferguson himself has spoken of the success that the diamond could bring for United this year, if they can effectively dominate possession and the midfield.
If it turns out we play the diamond consistently it would be revolutionary because it is going against our history. But the level of the game in England and Europe now is so high that making yourself unpredictable is going to be a strength.
Teams will have to think if we are going to use two out wide or the diamond because we have players capable of doing both things.
Without Kagawa or Cleverley in the starting side, the argument could be made that United did not possess the technical skill to pull off the diamond formation.
But I disagree.
Neither Giggs nor Carrick could get going in midfield, and they dragged the Red Devils attack down the field as a result. Had they been in the diamond, Hernandez could have been better used in attack, and van Persie would not have had to do as much defending as he did.
Both veterans are able to hold the ball and maintain possession, which is required in the diamond. And against a relatively weak attack like Norwich, United also possessed the defensive solidity to establish the midfield diamond.
It was just a shame the formation didn't get utilized by the Red Devils this weekend. The result might have been entirely different if it had been.
What did you learn from United's loss to Norwich City?
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