The Serbia international has found English football difficult to adjust to after playing in Spain with Valencia.
He has been confined chiefly to a substitute role with last season's top scorer Cameron Jerome preferred as the main striker.
But McLeish has faith in Zigic to eventually show his true worth.
McLeish said: "Nikola is still adjusting to the English game. It is hurly burly, 100 miles an hour.
"On the continent he is used to balls being laid up to him and cushioning it and laying it off and keeping the play moving.
"It is a totally different game to the Spanish system and also the Serbian system as well.
"The players tend to get lazy as well when there is a big guy in the team because they just launch it forward.
"But we've got to try to get into the right positions to give him the right service."
McLeish admitted: "Nikola has still got to find some sharpness in his touch and things like that.
"But I am sure he will make a contribution."