Stand-in boss Rob Page admitted the display was not good enough as Port Vale lost 1-0 to Rochdale in the Johnstone's Paint Trophy.
Joe Rafferty netted five minutes before half-time, his first goal in senior football, to give Dale their first win at Vale Park in 25 visits.
"We are very disappointed and we've told the players that performance was unacceptable," Page said. "Every time Rochdale got the ball they had a couple of options, but when we got the ball we didn't.
"This is one of the very few occasions since I've been at the club when we've had to have a go at the players for a lack of effort and enthusiasm.
"Our team didn't look like the same group of players who have worked so hard to get results. It's something we will have to address over the next couple of days.
"We do have to give some credit to Rochdale because they did a job on us and played well. But we should have been able to put a team out who were capable of beating them."