With Fernando Morientes cup-tied and Florent Sinama-Pongolle and Djibril Cisse both injured, Liverpool are short of striking options for their Champions League games with Leverkusen so Kewell could be drafted in as a second striker.
"Harry is a good player. If he works hard in the week there are possibilities for him," said Benitez.
"He was training hard, trying to regain his confidence and when he scored against Aston Villa in December he was playing better.
"After that he missed some more training sessions and was back in the same position. It is difficult for him and bad for us.
"He has a groin problem and then a problem with his achilles. When a player has been weeks without training sometimes you get that. Harry can be important for us, we'll see how he trains."