"There is a lot of work to do," said the Coach after Friday night's friendly at the Mestalla.
"In these types of games, against top class opponents, if you are not 100 per cent concentrated in defence and attack then you run many risks.
"The first two goals were down to childish errors. We cannot give this type of advantage to a team like Valencia, who were superior to us in every way.
"We played well at the start of the second half, but I didn't like a single thing about the defensive approach in the first half.
"If you do not defend and attack with all 11 players, then you'll never achieve success."