But he is not looking to bring in a new centre-back and has faith in Czech international Martin Jiranek to provide back-up for Roger Johnson and Liam Ridgewell.
McLeish said: "I think it will be a long shot for Scott to be back before the end of the season.
"Nothing has been totally confirmed yet but we are going to miss him for a long time.
"It's a blow and we wish the big fellow a successful recovery first and foremost.
"But I've got Jiranek. I brought Martin in just in case of an emergency and he is ready to step in."