Westerveld, who now works as an agent, told NOS: "I have been calling for years that a striker and a goalkeeper are the most important players in a team.
"Not midfielders or defenders, keepers have been undervalued and underpaid for years.
"It does not matter what kind of clause there is in a contract.
"Kepa is really very good, but €80m? I do not know if I'd commit that for him, he comes from Athletic, he has no international experience, I would have first tried for (Manchester United's) David De Gea, but I do not know if that was possible for Chelsea.