Valencia coach Gary Neville called his players' performance "unacceptable" after they were beaten 1-0 in a local derby by struggling Levante, who sit bottom of La Liga.
Neville's former Manchester United team mate Giuseppe Rossi took advantage of a lapse in the visiting defence from a throw in to volley in the only goal on 65 minutes and the hosts missed further chances to widen the scoreline, overpowering a weak Valencia.
"That was an indefensible performance, unacceptable, not good enough," Neville told a news conference.
"I apologise to the fans of Valencia because the very basic premise of a football match is that you run, fight and tackle as hard as the opposition. I can't defend what I've just seen and I have to take full responsibility for that."
Rossi's goal condemned Valencia to a third successive defeat in all competitions and seventh in 15 league games since Neville took over at the club, which finished fourth in La Liga last season under Nuno Espirito Santo, who was sacked Nov.30.
Neville's side have also failed to keep a clean sheet in every single game since he arrived.
Valencia, 12th in La Liga on 34 points, host Athletic Bilbao in the second leg of their Europa League last-16 tie on Thursday needing to overturn a 1-0 deficit from the first leg.
But Neville's focus was far from the European tie after the chastening defeat to neighbours Levante, who remain bottom of the table despite the win, three points away from escaping the relegation zone.
"If we have concentrated on the Europa League subconsciously in some way then it is a massive mistake because that defeat today in a local derby is nowhere near good enough," he said.
"It is unacceptable in this city for us to play like that in a game of such importance to the people, against your local rivals that are at the bottom of the league, who fought for every single ball and we weren't good enough."
Valencia captain Paco Alcacer also gave a scathing assessment of the team's insipid performance.
"We didn't play football, we were just on the pitch," he was quoted as saying in Valencia-based newspaper Super Deporte.
"We have to look at the game again because we did everything you shouldn't do in a match."