The 16-year-old midfielder, who became the Eagles' youngest-ever player this season aged 15 years 287 days, looks set to turn his back on Palace's offer of a professional contract and move to Juande Ramos' club.
The transfer will go to a tribunal if the two clubs cannot agree a financial package and Palace assistant boss Mick Jones insists the Championship side will not be short changed.
"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," 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."