Benitez said: "Harry will need some time to get back to his best, but this is an important season for him.
"Harry wants to be fit and playing again, he wants to show people that he can play and be a good player for Liverpool.
"He is disappointed with how it has gone for him during his time here, but he is a professional who knows what he is capable of and he wants to play. He has more confidence in his fitness now. Maybe in the past he didn't have that kind of confidence, but he does now.
"The fans have criticised him a little at times, but they see a player with Harry's talent, they realise he is good and they want him to perform better.
"If you are a good player and play for Liverpool, you have to expect supporters to say, 'Come on, play better'.
"I have to manage the situation and understand Harry's problems, but this is a season where he does have to play well.
"I see Harry as a key player to help Peter Crouch develop as our centre forward. We have different players with different qualities and abilities, but Harry is the main one who can get to the dead-ball line and put over the kind of crosses that Crouch likes.
"I know Harry can do this. When I arrived at Liverpool, I brought with me the memory of once seeing Harry play against Manchester United for Leeds at Old Trafford and he was fantastic.
"Leeds lost the game, but he gave Jaap Stam a lot of problems, and that is the Harry Kewell I want to see playing for Liverpool."