The game at St Andrews on Sunday could become his first start for Birmingham.
“I’ve felt in recent weeks that Christian was more effective as an impact player,” Birmingham boss McLeish 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.”
