The Blues have been tracking the 19-year-old centre-back for some time, with rumours indicating that a move has been close to completion for a while.
It has been said that personal terms between the club and the player have been agreed, and that Saint Etienne were willing to sell.
However, it has now emerged that the French side want a massive £18m offer to let their teenager leave.
Chelsea are reportedly willing to strike a deal now and let Zouma stay with Les Verts for the remainder of the season, but their demands are threatening to derail any arrangement.
Yet Saint Etienne are unlikely to back down, with co-president Roland Romeyer indicating that a transfer will not happen unless their valuation is met.
“Some clubs have launched a bid for the player, but we will not change our strategy,” Romeyer said.
“There have been discussions for Zouma with English, Italian and French clubs, but he will not be leaving this month unless we find an agreement with some of the potential buyers.
“If not, he will have to wait until the summer. We are under no obligation to sell.”