Kevin Nolan's last-gasp winner for the visitors condemned Blues to their second defeat in the space of three days and Bruce admitted that the busy festive period schedule seemed to have finally taken its toll on a weary looking Blues side against the Bolton.
"It was disappointing and cruel to lose like that," the Blues boss said after the 2-1 defeat at St Andrew's.
"We were out on our feet to be fair and the fixture pile-up that we've had has certainly hit us tonight.
"I'm not looking for excuses because Bolton finished the game better than we did but when you concede in the last twenty seconds like we did it knocks the stuffing out of you.
"We spent that much energy chasing the game in the second half when we were camped in their half for 30-35 minutes, piling people forward, grabbing an equaliser and looking like we may go on to win the game.
"But then we've then lost Clemence with cramp which disrupted us and gave the impetus to Bolton for the last ten minutes."
Bruce decided to leave midfielder Robbie Savage out of the squad for the game following his handing in a transfer request on Monday and the Blues boss explained his reasoning for this.
"I don't think his head could have been right after handing in his transfer request yesterday and I'm only interested in players who want to play for this football club," the Blues boss explained.
"I had a load of them out on their feet trying to do that tonight and I felt after the whole situation he'd be better left out."