Mourinho takes his side to Turkey to face Fenerbahce on Thursday having lost ground in the Premier League title race.
But United have six points from their three games in the Europa League and a second win over Fenerbahce would put them in a strong position to advance.
“My opinion changes because the rules change, and because the Europa League winner has a direct spot for the Champions League,” Mourinho told his pre-match press conference.
“In the last couple of years, the Europa League for the big clubs has a different meaning because it's another way to try to qualify for the Champions League.”
“I don't change my opinion that big teams belong in the Champions League with the history, but the Europa League is a target because you can qualify for the Champions League.”
Mourinho, who took over at United in the summer, has cut a dejected, at times angry figure in recent weeks.
But the former Chelsea, Inter Milan and Real Madrid manager said he had not lost his love for the job.
“Of course I'm excited and of course I'm not happy with results, that is obvious,” he said.
“What I am happy with is the performances. Sometimes you win matches but you feel that the period cannot last forever because the team is not playing well.
“Other times you have results where you feel the good results have to arrive sooner or later. I have a very good feeling towards the players.”
After losing 4-0 to Chelsea the team “reacted in an unbelievable way,” Mourinho said.
“The number of shots we had in the last match (a 0-0 draw with Burnley) was something absolutely incredible,” he added.
Original source: Mourinho taking Europa League seriously