Pennant believes the Spaniard's managerial style and cautious tactics have resulted in some high-profile players finding their best form elsewhere.
"I don't see how a player can play at an average team and be great and go to Liverpool and be not as great. It should be a lot easier," Pennant told the Guardian. "Liverpool have had some great strikers come and go - Robbie Keane is scoring goals at Tottenham, Peter Crouch is scoring now.
"It didn't happen at Liverpool: it must be about how the manager relates to players, how the tactics are and how he restricts players. The coach plays a big part when you arrive at a new team. If he restricts you, it's going to make you play differently."
Pennant insists his criticism of his former Reds manager is nothing personal.
"He's a great manager and there are times when he is a genius but sometimes his approach can take the best out of you. Liverpool are a great side but they need to let loose and express themselves a bit. Look at Barcelona - you don't see them restricted, you see them breaking all sorts of shackles and they win things. Maybe if Liverpool went that way a bit they would be even better."