The 54-year-old, with Thursday's second leg against Celta Vigo in mind, made eight changes from the side that won in Spain against Arsenal.
United, who hold a 1-0 lead from the first leg, will qualify for the Champions League if they win the Europa League, so Mourinho wasn't too concerned with the result against Arsenal.
Our options of entering the Champions League through the Premier League have decreased after this week, but we will keep on trying until the last game, first at Tottenham this coming weekend.
"But it's good to have the opportunity to play - the manager gives you a job and you have to show he can trust you for future games".
"Is it possible?" he began when asked about his side's top four chances this season following their 2-0 Arsenal defeat on Sunday afternoon-which itself came mere hours after Liverpool had drawn with Southampton to put United back in control of their own top four destiny.More news: Trump's frustration with budget compromise has him considering merits of a 'shutdown'
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"I am very happy with the players, they surprised me in a positive way", the manager added. "At the end of the day, that's what I make of it", he said. They had the luck of [the first] goal. The Arsenal fans are happy and I am happy for them.
"Arsène Wenger is not a small manager, he's a big manager - to have that record of winning so many matches [against him] is not normal".
The former Liverpool defender criticised Mourinho's negative approach that has seen them struggle to break into the top four. Because I don't think the others, playing one match per week and being in a great situation, are going to blow it. You think I enjoy the fact that a big club like Arsenal is not winning big trophies?
"Now we have only one point more, we wanted to have three points more, but it's not the end of the world", Klopp said. "So it's not normal and I really don't care about it".
The win also takes Arsenal within two points of fifth-placed United, who stay four points behind Manchester City having played the same number of games as their local rivals. "We couldn't afford to lose. We'll focus on Wednesday, thank you". Slowly I think we became better and in the second half we controlled the game quite well.