Ahead of their FA Cup clash with Manchester United, Redknapp said: "There's every chance for John to come back in and be involved at Manchester United. We are going to need some performances from him between now and the end of the season.
"He has all the ability in the world and can be what he wants to be. He can finish terrifically. You'd take John to score when he goes through. He has done that on a couple of occasions for us this season.
"John has fantastic ability so it's up to him to put it to use. He has to use it."
Redknapp added: "He could learn from Lassana Diarra. John is a laid-back lad. Lassana works on his game and wants to become a better player.
"Nothing is going to stop him from improving. He has a great attitude - like most great players."