Marcelino has conceded that it will be difficult for his team to turn things around next week, but the Spaniard has insisted that "the tie is still open".
"It was a strong performance from us but not a good result," Marca quotes Marcelino as saying. "It will be very difficult for us to progress but not impossible and we will try to be heroes, we believe the tie is still open and we have hope.
"Playing at the Mestalla will benefit us and the fans will be big, hopefully we will be the third team to shutout Barca this season."
Valencia have won the Copa del Rey on seven occasions, with their last success coming in 2008.