"It is more likely that Robbie will make an impact like Thierry Henry did for Arsenal so Robbie won't start," he told the club's official website. "He'll just come on and score instead! I've told him that.
"He would be desperate to start, but I have to be fair to my own players and those who are here for the long term.
"I don't think any of them have done too much wrong. We could do with getting our strikers back in the goals and if Robbie is here to shake it up then great, but he has a part to play also."
The Midlands outfit currently trail opponents Everton by one point in the Premier League.