And he revealed that O'Connor is struggling to overcome a groin problem which first flared up last season when Blues gained promotion from the Championship.
McLeish said: "To say Garry is lazy is absolute nonsense and he has been playing with sore groins.
"He had the operation last season and you should remember some of his performances in the Championship. All of a sudden he was cut down with this groin problem.
"This season Garry is struggling with the whole mobility thing.
"But we are doing rehabilitation exercises with him, preventative measures, and I am sure Garry will have a big contribution to make.
"He has already scored the winner for us at Hull and, if that kind of stuff doesn't satisfy some people, then what chance have you got?"
McLeish saw Blues register their third victory of the campaign last weekend - against Sunderland at St Andrew's - after reverting to a 4-4-2 system.
But the former Scotland boss is adamant he may again revert to playing with one striker in the future.
He said: "When you lose your home games, and before last weekend we had lost two on the trot, people have every right to pick apart your system if they feel you are being negative.
"I keep assuring people we have not been trying to be negative with one up front. We've picked five midfielders who are decent with the ball and we thought we could get better support to the front man.
"Losing kills you. Tony Mowbray is getting the same at Celtic, like when he plays one up front at Ibrox (against Rangers), but he is looking for control of midfield.
"It is different between playing totally defensive and trying to go and support the front man. If we can get the complete right personnel, we can still play that system."
On-loan Sunderland midfielder Teemu Tainio should be available for Saturday's home clash with Manchester City.
He was ineligible to face the Black Cats last weekend but McLeish hopes the extra week's rest will enable him to fully shake off a hamstring problem.
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