The Spanish team, who are behind 3-0 from the first leg, will face United at Old Trafford tonight.
Yeray said in a media preview that the team believes anything can happen in football and that they have worked hard to prepare for the match.
He added that every player's dream is to play in a game like this, and that the team is motivated to give it their all.
Yeray also emphasized the importance of pressing and generating chances, citing the dismissal of Dani Vivian in the first leg as a key factor in the loss.
He said that the team needs to press United up front and create as many chances as possible to turn the game around.
Yeray also acknowledged that the team will be missing some key players, including the Williams brothers and Oihan Sancet, but stressed that the remaining players are still strong and motivated to win.
He said that the substitutes are eager to play and will give everything they have to help the team succeed.