Christian Benitez is set to be handed his first Birmingham start in the Premier League derby clash with Aston Villa at St Andrews on Sunday.
The Ecuador international, who was signed on an initial season-long loan from Santos Laguna, has done well during his substitute outings during the opening weeks of the season.
Striker Benitez has been working his way to full fitness after an operation on his shoulder early in the summer.
And McLeish is intimating he will now promote him to the first XI for the clash with Martin O'Neill's side.
"I've felt in recent weeks that Christian was more effective as an impact player," the former Scotland boss said.
"But that may change in a week's time (against Villa). If I can't play him at home, then I will never play him.
"I am pleased with his introduction so far and we have worked hard on his fitness.
"When he came here, he was behind the rest - along with Giovanny Espinoza - in fitness terms.
"Christian is at a good level now and looking dangerous and I think he is going to be a great acquisition to the club."
McLeish will check on Benitez's physical condition when he comes back from a World Cup double header with his country before making a final decision.
He was in action in Colombia at the weekend and Ecuador will tackle Bolivia in midweek.