In a clear reference to his own injury-prone squad, Houllier insists that no side can compete at the highest level without their top players being consistently available for selection.
Houllier said: "I feel sorry for Bobby Robson. I know what he is going through. When you don't have your major players available it's very difficult to compete at the top. Even the likes of Manchester United have struggled when Van Nistelrooy has been missing."