Alex McLeish admitted he was disappointed with the performance of some of the Birmingham City players he gave a chance to during Tuesday's Carling Cup last 16 victory over Brentford.
The Blues were indebted to Kevin Phillips after his 92nd minute effort set up extra time against the League One outfit.
The Premier League side eventually progressed on penalties after a side that showed seven changes from the weekend struggled to gel.
"Although they train with each other every day, it's sometimes very difficult and you can see there wasn't great cohesion out there at certain points of the game, so that's what can make these games difficult," explained McLeish.
"The first half was okay. We knew Brentford would be really organised and they got bodies back behind the ball and the first half was very even, but we thought maybe we could tire them in the second half and move the ball about.
"But there was just a lack of that imagination and creativity that really made it look as if we wouldn't score, although getting the substitutes on made a difference.
"Kevin did what he does best, we're in the hat and that's what counts.
"We're in the quarter-finals and it's all part of the development of the club."