Pennant was dropped to the bench for his side's 2-1 defeat to Hull City on Tuesday night after failing to impress his new boss since his loan move from Stoke, and Solbakken has told the winger that his form needs to improve.
"I think it's normal what happens when he hasn't played for a while, maybe you struggle a little bit for the match rhythm," the Birmingham Mail quotes the manager as saying.
"But he has had some good moments. I think, also, for many players coming into this league from the Premier League, if you stay on the ball one second too much then you are up in the air.
"It's very normal after playing three quick games after a spell out but now his excuse is up. He must start producing."
Pennant may be recalled to the starting lineup against Brighton & Hove Albion on Saturday.