United go into Sunday’s derby against Manchester City off the back of two last-gasp wins away from home, over Bournemouth and Juventus in the Champions League.
But he warned that unless they start better against Pep Guardiola’s free-scoring leaders they could find the mountain too much to climb even with what is becoming a customary late rally.
“In a positive way it is easy to feel we are a team that does not give up, always find a way to fight back, sometimes changing results,” said the United boss.
“But going to the other side you can ask why we always concede before the opposition. There will be a day where we cannot come back, so we have to grow up in our approach.
“It is clear the team is growing up, but we have to grow up in our compactness and start matches well.”
Mourinho’s side could slip 12 points behind City if they are beaten in the derby but can at least draw inspiration from the fact they won the last meeting between the two sides on blue soil.
On that occasion, in April last year, a come-from-behind win for United, going two down inside the first half-hour but winning 3-2, forced City to delay their title celebrations.
“It is not special because of what happened last season but it is special because it is a Manchester derby,” he said. “If we drew it is nine points between us, if we lose it is 12, but we have to just think about the match which will be a difficult match against a difficult team. But they will be thinking the same.”
Romelu Lukaku, who has missed the last two games with a hamstring injury, will train with the team this morning before Mourinho makes a final decision on his line-up.
City boss Pep Guardiola is hoping his side can finish a difficult week off the field for the club on a positive not on it.
But asked once again about allegations of financial impropriety exposed in a German news magazine this week, he admitted if City have transgressed rules it is right they should be punished.
“I trust the people at the club and, if there’s something wrong, we’ll be punished,” he said. “So whatever FIFA or UEFA say we were wrong we will have to accept it.”