Manager Jose Mourinho says Manchester United will lose matches if his team do not "grow up" and "start matches well".United rallied from 1-0 down to beat Juventus 2-1 in the Champions League - the fourth time they have come from behind to avoid defeat this season.
Mourinho's seventh-placed side face Premier League leaders Manchester City at Etihad Stadium on Sunday.
"If we keep conceding goals before the opponent, there will arrive the day where we cannot come back," he said.
United were 2-0 down to Newcastle on 6 October but won 3-2 while against Chelsea two weeks later they conceded the first goal but fought back to draw 2-2.
Against Bournemouth last weekend Marcus Rashford's 92nd-minute goal saw them win 2-1 despite conceding in the 11th minute.
In Turin on Wednesday, Cristiano Ronaldo put Juventus ahead but an 85th-minute free-kick from Juan Mata and an Alex Sandro own goal four minutes later saw United complete a famous comeback.
"We are not a team that gives up," said Mourinho. "We are a team that always finds a way to fight back.
"We have to make sure that we grow up, not just in our approach because I think it is clear that the team is growing up, but we also have to grow up in our compactness and to start matches well."
United could be bolstered by the return of Romelu Lukaku on Sunday, with the Belgium striker missing the Bournemouth and Juventus games through injury.
"Lukaku is training with the team this morning," said Mourinho. "If the answer is positive and we have, of course, one more session tomorrow, but if the answer is positive then he is ready."
United finished second in the league last season - 19 points behind City - and this campaign they are seventh, nine adrift of Pep Guardiola's side. The last meeting between the sides in April saw United come from 2-0 down at half-time to win 3-2 and delay City clinching the title.
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"We are going to try. I cannot say that we are going to be successful in our motivations and desires," said the Portuguese.
"But we played two difficult matches away against two very good teams, Chelsea and Juventus, and we managed to get good results.
"Even if the good results were not in our pockets, the performances were there. The positive attitude was there, so we are going to try.
"I don't think it [the Manchester derby] is special because of what happened last season. It's special because it is a Manchester derby and it means what it means."
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