Head coach Nuno said he was "ashamed" of Valencia's display after they were beaten 1-0 by Gent in the Champions League.
A 49th-minute penalty from Sven Kums secured a first-ever victory in the competition for the Belgians and kept them in contention to qualify from Group H.
Valencia could have booked their place in the last 16 with victory but managed just one shot on target in a below-par performance.
"We had a really bad game, especially in the first half when we were just as aggressive as the opposition but hardly created anything", Nuno is quoted as saying by Marca.
"We're ashamed of our performance. We were overrun. We were nothing like the team we have been and want to be in the future.
"Our image and performance out on the pitch was a far cry from what we want it to be, or what we expect from a team representing a club like Valencia."
The Spanish side are second in the group, two points ahead of Gent and six behind already-qualified Zenit St Petersburg.
Their next game sees them travel to Russia to take on Zenit while this Saturday they go to La Liga high-flyers Celta Vigo.