Such high hopes for Kewell have, much like thoughts of a Liverpool title challenge, been dashed in a turbulent season on Merseyside, but Rush feels the 25-year-old can hit back against Manchester United this Saturday.
Rush said: "Harry Kewell has been the first to admit he's not been happy with his form this season, but I wouldn't bet against him making a difference against United.
"I know Harry well and he's an honest player. What he's lacking at the moment, and has been since he came back from injury, is confidence.
"But he's still a class act and a manager is always likely to persist with players like him because it only takes a split second for all the self-belief to come flooding back.
"Harry has the ability to score a stunning goal or deliver a defence-splitting pass. At a venue like Old Trafford, you can also be certain the opponents will still be worried about what he could do to them."