The Blues had taken an early lead through Nikola Zigic, but Marcus Alonso equalised before a Keith Andrews penalty and a Chung-Yong Lee strike consigned Clark's side to a 10th defeat of the season.
Zigic was shown a second yellow card in the 89th minute to round off a miserable afternoon for City, and Clark focused his anger on his senior players.
He said: "We didn't play well at all. It was our most inept performance for many weeks.
"We allowed (Jay) Spearing and Andrews to dictate the game, which was what we had planned not to let them do.
"I heard a few rumblings from our supporters that we should be playing four-four-two, but (after Zigic was sent off) we now don't even have a fit or available striker for the next match, so how are we meant to do that?
"I'm absolutely furious with that performance and I'll be working hard to address it.
"I'll play 11 teenagers if I have to. I know there is a fine crop of youngsters here who are ready to play and if the senior guys aren't up for it then they won't play.
"They can help the club kick on and I'd prefer to keep all those young lads than to keep hold of players who don't want to be part of the club."