Ferguson used to be a prolific marksman during his days at Rangers but has been asked to alter his game since moving to Blues in the summer in a £1million deal.
McLeish said: "Barry used to score a great number of goals at Rangers. I think he got 18 when we won the treble one season.
"He used to make a lot of forward runs and we had fantastic players who could make the most of him getting into good positions.
"We have asked him to modify his game since he came here and it's been Lee Bowyer who has been getting a fair share of goals. But that was vintage Barry, with the run and finish."