A dejected Louis van Gaal admitted the Europa League is now Manchester United's best hope of a Champions League return following Saturday's 2-1 defeat to Sunderland.
United were punished for a poor display at the Stadium of Light, with a late own goal from David de Gea handing Sam Allardyce's side all three points after Anthony Martial had cancelled out Wahbi Khazri's opener.
Van Gaal is refusing to abandon hope of a top-four finish in the Premier League, but, with his side six points adrift of fourth-placed Manchester City after playing a game more, the former Netherlands boss conceded focusing on the Europa League could now become a priority.
"You have to win this kind of match, I said that in advance. We didn't do that," he said.
"It's still possible [to finish in the top four], but it's very difficult. The way through the Europa League is easier, I think, but there is a fantastic European level in that cup. You have to fight for it.
"We needed the points so much, everybody knows that. In the circumstances, it's very disappointing.
"We needed to win this game. It's not a question of [being] let down, the players want to deliver. But because they don't deliver, you're disappointed and frustrated. But we're working together, pulling at the same string.
"You have to show your capacity in every match and we didn't do that."
Wayne Rooney criticised United after the match for failing to match Sunderland's competitive edge and Van Gaal echoed his captain's assessment, insisting his side should have done more to take control of proceedings.
"What's most disappointing for me is that we couldn't cope with the aggressive pressure of Sunderland in their own half," he said.
"We didn't keep the ball. You can control the game when you keep the ball. You have to do it in spite of the pressure of Sunderland and create chances.
"But we didn't have control, what you've said is the truth. We didn't control the second half or the first 20 minutes of the game. In the second 20 minutes, we had control and we scored.
"We knew in advance that they could score out of set-plays, they have the taller team. But the main reason is that you'll always be compared with your opponent in aggression and they played with more aggression. They won a lot of second balls.
"We could cope with that aggression, we had our positional game and we scored a fantastic goal, but in the second half, Sunderland were even more aggressive. We lost a lot of balls unnecessarily in the second half.
"It's a big disappointment. I cannot say it in another way. You prepare this game all week and then it's always the big question if you can cope with the tactics, aggression, some quality of the opponent and you have to show your own quality against that. It was very disappointing."