Manchester United will face a knockout round playoff in the Europa League despite recording a 1-0 victory over Real Sociedad in Thursday's contest in Spain.
The Red Devils entered the match knowing that they needed to win by two goals in order to finish ahead of the Basque outfit at the top of Group E.
The two teams have ended their group-stage campaign level on points (15) and also boasting the same head-to-head record, but Real Sociedad's superior goal difference has allowed them to automatically advance to the knockout round, while Man United will have to face a Champions League dropout over two legs in February, with Barcelona and Juventus possible opponents in Monday's draw.
Alejandro Garnacho's first goal for the Red Devils decided the contest, but the 20-time English champions could not find the second that they needed in San Sebastian.
Carlos Fernandez fired one into David de Gea's side-netting in the fifth minute, with Real Sociedad on the front foot early on, although the offside flag would have stopped the home side from taking the lead from that attack, had the ball found the back of the net.
Man United made the breakthrough in the 17th minute of the contest when Cristiano Ronaldo's brilliant pass released Garnacho, and the youngster picked out the back of the net with an excellent finish.
Garnacho had another opportunity in the 27th minute after finding himself inside the Real Sociedad box, but the teenager, who showed clever feet to work the space, fired over the crossbar.
Pablo Marin hit one from distance in the 32nd minute, as the home side looked to answer back, but his effort was always moving side of De Gea's goal, before the youngster rolled one into the arms of the Man United goalkeeper five minutes before the break.
Ronaldo had a golden chance to score a second for Man United in the 42nd minute, but the Portugal international's chipped effort landed on the top of the goal.
De Gea then made two excellent saves to keep the score at 1-0, with the second from Marin a stunning stop, as he reacted quickly after getting down to keep out the first effort from Andoni Gorosabel.
Real Sociedad again came close early in the second period through Alexander Sorloth, but the striker's header was deflected over the crossbar by Lisandro Martinez, before Brais Mendez missed the target shortly after.
Marcus Rashford and Scott McTominay were introduced for Man United just before the hour, with the visitors going to a back three in search of the second goal that was required.
Fernandez fired over the away side's crossbar in the 70th minute before De Gea had to keep out a low strike from Ander Guevara during a strong spell for Real Sociedad.
Sorloth then struck wide of the target in the 78th minute, before Harry Maguire and Fred were introduced for the visitors, with the Man United captain going into a forward area.
There was to be no second goal for the Red Devils, though, despite some late panic inside the home side's box, with Real Sociedad qualifying for the knockout round on goal difference, leaving Erik ten Hag's side needing to navigate a two-legged knockout round playoff in order to progress in the competition.
Next up for Man United is a trip to Aston Villa in the Premier League on Sunday, while Real Sociedad will welcome Valencia in La Liga on the same afternoon.
