Anderlecht sporting director Herman Van Holsbeeck has told Everton that they will have to pay in excess of £15m to sign midfielder Youri Tielemans.
The highly-rated Belgian has attracted the attention of a number of European clubs, but he has previously talked up a switch to Goodison Park.
However, the Toffees have been warned that they will have to pay more than the £15m which Leicester City spent on Genk midfielder Wilfred Ndidi during the January transfer window.
Van Holsbeeck told VTM Nieuws: "It will have to be much more than the €17m (£15m) Genk received for Wilfred Ndidi.
"I have a sum in my head but I will not say. Everything depends on the clubs to come. I think a transfer must always be a win-win situation.
"For the player, the club that buys and the club that sells. His entourage has always been correct with us, so we will be right with him."
The 19-year-old Belgian international has already made 156 appearances for Anderlecht, scoring 28 goals.