Peterborough manager Dave Robertson says he "can't keep defending" his players after Tuesday's 1-0 Johnstone's Paint Trophy defeat at Millwall.
The loss means Posh have only won three of their last 16 games.
"Very harsh (words were said). I was honest with the players on what they need to do," Robertson told BBC Radio Cambridgeshire.
"That's something, simply, I demand as a manager, but more importantly what the football club demand from them."
Robertson, who took full-time charge of Posh in the summer after a spell as caretaker, has seen his side take four points from their opening five league games.
They have struggled for goals from their forward players, with only winger Marcus Maddison scoring more than one so far this season.
And Robertson says his players need to learn to take their chances following the defeat at The Den.
"We had some real good opportunities which we didn't take and ultimately that's cost us, as well as players, I can't keep defending them, quite simply they didn't work hard enough for the team," he continued.
"They've got to understand their role within the team and be part of the team - that's cost us a sloppy goal.
"The game for me was not a great game, we've created 14 or 15 chances but we've got to take them - too many players let us down."