Defoe has scored just two goals in the last 11 matches.
Redknapp said: "We need a performance from him. In the first half of the season he was fantastic, just unplayable. I don't know with Jermain. Hopefully he'll finish the season well with two games to go.
"If he gets his chance he'll take it. He has still got a lot to play for.
"He's got to get into that England squad, there's no certainties with any of them apart from Wayne Rooney.
"I think all the other places up front are probably up for grabs, so Jermain and Peter Crouch have got a lot to play for."