Carr arrived at St Andrews this year after over 12 months out of football following a release from Newcastle United.
"There's no doubt he's been a really tremendous acquisition," acknowledges McLeish, "after plucking him from nowhere I suppose, when he had announced his retirement.
"He reads the game well and that's his experience.
"He's a quality defender and he very rarely loses in the air at the back post. He's great at getting his body into the forwards and he's got a good spring himself, but his engine - he's got a fantastic capacity to go up and down the pitch."