Portsmouth fullback Djimi Traore has suffered a serious hamstring injury on-loan at Birmingham City.
McLeish does not now expect the defender to be available again until much later in the season.
"Djimi has got a grade (two) hamstring tear - with grade one being the lowest," McLeish told the club's official website. "You're now talking six to seven weeks."
Traore has been plagued by injuries throughout his career and McLeish is disappointed on his behalf.
He explained: "We said at the time we signed Djimi 'let's see if he can prove his fitness and show that he's over all his injuries', but the curse has struck again. It's a shame and a blow for him.
"I don't think he's had a hamstring problem for about a year now. We did know there was an element of risk there, but it seems indicative of the bad luck that we're having injury wise at the club in recent times."