Redknapp's struggling QPR travel to Stamford Bridge on Wednesday to face their London rivals, who earned a hard-fought victory over Everton thanks to a double from veteran midfielder Lampard.
The England international's current deal with Chelsea expires in the summer, and with a new agreement yet to be reached, speculation regarding the 34-year-old's future has been rife. However, Redknapp - who managed Lampard, his nephew, during his time at West Ham - believes the Blues would be best served by agreeing terms on a new contract for the midfield talisman.
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He told the Daily Mirror: "I personally think they would be making a big mistake in letting Frank go. I don't think you'll find anywhere a better attacking midfield player who will score more goals in the Premier League.
"I don't think they can upgrade from Frank. He is an amazing goal-scoring midfielder, so I still think there is every chance that he will still be at Chelsea next year.
"I think the importance of age can be overstated. I've said many times he is the best trainer I have ever seen in football, without a doubt. I saw him as a 16, 17-year-old - when all the other kids had gone home, he would be practising every day. I've never seen anyone even come close to him.
"He's still in great shape and has still got that desire. Frank just gets on with it. Every club needs players like that, but you can't put it into people, they have to want to do it."