The striker is currently on loan from Manchester City, who Redknapp believes are paying most of his reported £170,000 per week wages.
"If Emmanuel maintains his current form I would love to keep him, but his wages are going to be a major stumbling block, that's for sure," he said.
"I have no idea how much we are paying towards his wages at the moment as the chairman (Daniel Levy) deals with those issues but I suspect they are massively subsidised by City.
"The only way we can realistically get a deal done is if Emmanuel is prepared to take a substantial pay cut and put his football before money."
Spurs resume their Premier League campaign on Sunday away at Newcastle United.