Marcelo says Real Madrid's attitude was all wrong for their Copa defeat at little Alcorcon last week.
The Brazil international impressed for Real in Saturday's win over Getafe.
But on the 4-0 Copa defeat, Marcelo said: "Against Alcorcon we did not go out on the field with the spirit needed to win the game.
"And I'm not talking about one or two, but everyone. We knew it was a difficult pitch and it was. We went asleep. Of course it's possible to comeback. It will be very difficult, but I am convinced we can win the tie."