He would love to sign the striker on a new deal but admits wages of around £200,000-a-week paid by City would be impossible to match.
Redknapp said: "I'd be talking rubbish if I said people wanted to stay at Tottenham because we play good football.
"If you want to keep the best players, we must find a way of doing a deal that's near to what they can earn elsewhere.
"We're not in a position to pay £40million or £200k-a-week, we don't do it.
"The chairman Daniel Levy doesn't run it like that and rightly so."