Alejandro Garnacho's goal gave Man Utd a 1-0 result over Real Sociedad in the Europa League but Erik ten Hag's side still finish as runners-up.
Manchester United will face a play-off to qualify for the last 16 of the Europa League after beating Real Sociedad on Thursday but still finishing second in Group E on goal difference.
The Red Devils needed to win by two goals to leapfrog Real Sociedad at the top of the table and looked on course when Garnacho made it 1-0 on 17 minutes with his first senior goal for the club.
Cristiano Ronaldo should have doubled the Red Devils' lead but wasted a glorious opportunity before David de Gea produced two great saves to preserve his clean sheet.
The second half was more chaotic and ended with Ten Hag throwing on centre-back Harry Maguire in attack in a desperate search for that crucial second strike.
The goal never came which means Man Utd will now face a team dropping out of the Champions League for a place in the knockout round.
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Alejandro Garnacho
Manchester United's highly-rated teenager was a surprise starter against Real Sociedad but did not disappoint in an exciting performance.
The 18-year-old had a night to remember by scoring his first senior goal for the club and was the Red Devils' biggest threat in the Basque country.
Garnacho showed electric pace and superb composure for his goal, and Manchester United will be hoping it's the first of many for the Red Devils.
David de Gea
Real Sociedad looked certain to equalise just before half-time in what would have been a killer blow to the visitors just before the break.
However, De Gea again came to the rescue with two brilliant saves that ensured the team would head into the second half still with a chance of topping the group.
Andoni Gorosabel was the first to be blocked by the stopper who was at full stretch to deny the right-back. The ball then broke to Pablo Marin who saw his effort blocked by De Gea.
United couldn't quite get the job done on the night but De Gea certainly did all he was asked.
Lisandro Martinez
The Manchester United defender continued his fine form with another commanding showing at the heart of the defence
Martinez was again partnered with Victor Lindelof and impressed not just with his non-nonsense defending but also his ball-playing abilities.
The only bad news for Manchester United was the sight of Martinez picking up a booking that will rule him out of their next Europa League match.
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Donny van de Beek
The Dutch midfielder was handed a very rare chance to impress against Real Sociedad after surprisingly being named in the starting XI by Erik ten Hag.
But the 25-year-old looked rusty and the game largely passed him by. Van de Beek simply couldn't get going and was gone and back on the bench before the hour mark.
It was very much an opportunity missed for Van de Beek and it's unclear when he will get another chance in the first team at Old Trafford.
Cristiano Ronaldo
Ronaldo did well to tee up Garnacho for Man Utd's goal but the Red Devils needed much more on the night and the Portugal international could not serve it up.
The 37-year-old did have a great chance to make it 2-0 but passed it up in the first half. Ronaldo made the right choice in opting for the dink but put too much on in and saw the ball bounce onto the roof of the net.
Ronaldo then found himself in a rather bizarre situation of being partnered by Maguire for the final minutes as Ten Hag went route one in a desperate search for a second goal that never came.
He can feel good that his performance level has ticked up slightly, but a dramatic goal would have been so sweet.
Champions League drop-outs
Manchester United's failure to win the group means they face a tricky test getting into the knockout stages of the competition, unlike Real Sociedad who progress straight to the last 16.
Ten Hag's side will now face a play-off against one of the eight teams dropping out of the Champions League after finishing third in their groups.
It's not a great situation for Manchester United or their prospective opponents who surely won't relish coming up against the Red Devils over two legs.
United may not be the force of old but are improving under Ten Hag and are not a team that sides such as Barcelona, Ajax or Sporting will relish being drawn against.
GettyMan Utd Ratings: Defence
David de Gea (8/10): Caught the eye with a brilliant double save just before half-time to prevent Real Sociedad equalising.
Diogo Dalot (7/10): Another strong showing from Dalot who continues to shine at right-back.
Victor Lindelof (7/10): Solid again alongside Martinez in the heart of the defence.
Lisandro Martinez (8/10): Another commanding performance in the heart of the Man Utd defence but picked up a booking which means he’ll miss their next match.
Luke Shaw (8/10): A good all-round performance from the left-back.
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Casemiro (7/10): Another influential performance from the Brazilian in midfield.
Christian Eriksen (5/10): Neat and tidy but not quite his usual impact.
Donny van de Beek (4/10): A surprise starter but looked rusty and struggled to get into the game. A missed opportunity for the Dutchman who was hooked before the hour.
