Mourinho admits United fans still remember the defeat at FC Midtjylland last season.
"What happened against FC Midtjylland is what fans cannot forget. Maybe as a player, but the fans cannot forget it. We must be sure that we face them up for the fight," said Mourinho.
"We're going to win the match. We will win the tournament. It will be difficult, but it is quite simple to have it that way and say it.
"It is the mission we go into the tournament with."