The 16-year-old midfielder looks set to turn his back on Palace's offer of a professional contract to move to White Hart Lane and the transfer will go to a tribunal if the two clubs cannot agree a financial package.
"The sensible approach is for our chairman to speak to them directly but if the figures can't be negotiated we will go to tribunal and our evidence is fabulous," Palace assistant boss Mick Jones told the South London Press.
"The situation has now gone from personal warmth to being a business one and John has been with the club since the age of seven, in the first-team at 15 and been captain of England Under-17s. That is proof of the potential he's got.
"There is also no dispute he's gone to one of the top clubs in the world and that is also relevant. With all due respect, if he was moving to Wigan it would be a different ball-game.
"They must rate him highly and he can't come cheap. It should all stack up well in our favour."