Manager Andy Hessenthaler has slated Gillingham's "criminal" defensive display after they let a 3-1 lead slip to lose 4-3 at home to AFC Wimbledon.
The Gills have lost four of their last five games, slipping out of the League Two play-off zone in the process.
He told BBC Radio Kent: "It's not acceptable. That's two weeks in a row now. We just can't defend like that.
"It was schoolboy defending. It's got to stop and it's got to stop now or this season will fizzle out again."
Gillingham are poised to recall 19-year-old Connor Essam from his loan spell at Dartford, despite the centre-back having never made a first team appearance.
And Hessenthaler, 46, refused to rule out making more alterations to their back line.
"We've got 20 games to go. Do I need to do something about it defensively? I think I do, yes.
"I cannot accept that. We've got a 24-hour recall on Connor Essam. He's been doing really well," said Hessenthaler.
"I'll call the lad back, bring him in and put one of the younger ones in there. We just can't defend like that."
In order to eradicate their defensive woes, Gillingham were called in for extra training on Sunday ahead of two midweek friendlies against Millwall and West Ham.
And BBC Radio Kent understands that the majority of the players responsible for Saturday's defeat will be involved.
Hessenthaler fears that if Gillingham continue to leak goals, it will all but extinguish their hopes of gaining promotion back to League One following a two-year absence.
"I cannot mess around. We need to achieve something this year. We need to react quickly and get it right.
"The minimum for us this year would be the play-offs. We still have to aim for the top three."