"To be fair, probably Geremi's done more of a job than me about him overcoming the problems he had," Allardyce told the Shields Gazette.
"I've obviously helped in that department, but no more than him, in saying 'why do you want to go anywhere other than Newcastle?', and the answer to that is there is nowhere else.
"We've resolved that by giving him a new contract and telling him that he can play in a number of positions.
"If you've got a Newcastle shirt and you're on the teamsheet, what more do you want?"
Allardyce added: "He's gone and taken the left-back spot, which has been really tricky for us and for the club for a long time, and he's filled the spot and done exceptionally well while Jose Enrique's been getting up to speed.
"There's no saying Jose can take his place now.
"(Against West Ham), Charles moved up a space and looked very threatening from a wide left position. He contributed a lot, and I'm very excited about this young lad.
"He's a big, big player for us as far as I'm concerned."
N'Zogbia signed a new, five-year contract earlier this month, keeping him at St James's Park until 2012.