This term, the 33-year-old has started all but one of the club's matches in the league and has impressed McLeish with his performance level.
McLeish is delighted with the former Republic of Ireland international's contribution and believes his experience has been invaluable in the club's bid to steer clear of the drop zone.
"There is no doubt Stephen has been a really tremendous acquisition for us after plucking him from nowhere when he had announced his retirement," said McLeish.
"His defending has been first class and he has been terrific for us and his experience is also valuable. Stephen is a quality performer.
"He very rarely loses a challenge in the air at the back post, but has also shown a fantastic capacity to get up and down the pitch.
"I have been absolutely delighted with what he has brought to us since coming here."