The French striker has netted 10 goals for the Magpies this season on loan from the R's after joining the west London club from Marseille for £8million in January 2013.
His form in the northeast, according to Redknapp, should have increased his price tag to £16m and the Loftus Road boss feels Alan Pardew should sign now before he misses out.
"You would think they would want to snap him up because, if they don't, somebody else will for that money," Redknapp told getwestlondon.
"We paid £8 million and he's worth double that because of the goals he's scored in the Premier League.
"He would be a great player if he came back, but he wanted to go. He's not going to want to come back here and play in the Championship. If someone came in and offered £16 million for him, I would sell him if it was my choice."
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