La Real currently have no points in their Champions League group, and Prieto has said that they intend to go to Old Trafford with designs on attacking the Red Devils.
"We are going there with zero points and we need a good result so as to stay alive in the group, to give us hope," he told reporters.
"If we are defeated, then qualification to the next round would be very complicated, so we will compete, try to get the win and to play a great game.
"We should give value to [the fans'] effort and the money they are spending in travelling out there. We will see if we can offer them a good game and dedicate a victory."
Elsewhere in the group, Shakhtar Donetsk take on Bayer Leverkusen.