Chris Wilder acknowledged his side had again been made to pay for missed opportunities having exited the EFL Cup at the hands of Crewe Alexandra on Tuesday night.
Speaking after seeing two goals from Ryan Lowe, including one in extra-time, condemn his side to a first round exit despite Leon Clarke scoring his first competitive goal for United, Wilder admitted he was bitterly disappointed.
The boss remarked: "We had opportunities, yet again, to put the game to bed - particularly one late on.
"But if you don't take them it always gives the opposition a chance and that is what has happened.
"We are disappointed because it is two losses on the spin. Some of the forward players will be frustrated they have not got on the scoresheet too, because we had numerous chances.
"At times we have played some good stuff but at times we have went into individual mode and didn't play as a team.
"Individuals went away from a team plan. We have to work within a structure. We want players to make good decisions as individuals but within our structure."
Wilder added: "There is a hell of a lot of work to do, together we have to recognise that we work better as a team."
"It was an open game, we want to go at teams, we have said that all along, but when it is open we have to be ruthless and we haven't been again - similar to Saturday there were balls flying across the box and we've not picked out that final run and converted our chances."