Anderlecht chief executive Herman van Holsbeeck said: “Dendoncker is the centrepiece of our defence. If we let him leave it has to be for a lot of money. We also have to find a replacement for him, even if it is a loan for six months.
“A deal can be done if the interested club puts 25 or 30million euros (£22m-26.5m) on the table for him. I’ve experienced plenty of difficult transfer windows, but this one is the trickiest of all.”
West Ham are said to have tabled a bid £16m to the Belgium team which was later increased to £17m.
Reports suggest Anderlecht will let Everton sign him as long as they agree to loan Dendoncker back for the rest of the 2017/18 season. Henry Onyekuru is already on loan at the reigning Belgian champions from Goodison Park.