Stoke were knocked out of the competition by a Adam Nowland 32nd minute goal at the Britannia stadium on Tuesday night and missed out on a money spinning tie at Birmingham City in the next round.
"We were very, very poor. We started at a slow tempo and could just not get out of that mode," the Stoke boss said after the 1-0 defeat.
"I can only apologise to the fans. We've also lost the chance to boost our coffers and that's very disappointing."