Neal Ardley lamented defensive mistakes in Dons 3-2 home defeat to Sheffield United - and stressed loyalty to his troops will only go so far.
Billy Sharp, Mark Duffy and Matt Done goals gave Chris Wilder's side their third league win on the bounce.
Ardley said: "We are very very disappointed with the way we have defended today. I mean it's poor. I've looked at some of the aspects back and we had our warnings.
"I've looked at the goals back and it's unacceptable defending on all accounts not just the back four it's midfielders as well.
"We came up against a strong Sheffield United team who are beginning to find their feet at this level but to defend the way we did as a team was poor."
Dons twice halved the deficit with Dominic Poleon's goal just before half time and then substitute Tom Elliott scoring to ensure a tense finish at the Cherry Red Records Stadium.
The AFC Wimbledon manager continued to express his frustration.
He added: "All three of their goals was not on the training field and not something they've worked on.
"I've talked a lot about responsibility on the pitch to dictate what we've worked on and set up systems to make sure we know how our opposition are going to play."
Despite a promising opening the class of the Blades did eventually tell, but the Dons manager made it clear that if players on the pitch aren't capable of doing what he asks, he will find those that can.
"I'm not sure the players have realised we've stepped up a level and because of that we've found ourselves not winning games and losing games," he said.
"We work really hard on defending with our match analysis and basic principles in the way we defend but we're not showing it enough.
"With the guys I've got to keep working hard on it but if players don't do it then I've got to find players that will do it.
"It's too much of a reoccurring thing and loyalty will go out of the window if players aren't performing."
