Bayer Leverkusen have made a contract offer to the Belgian.
His father and representative, Vic Alderweireld, told De Telegraaf: "The proposal [from Leverkusen] was interesting in sporting terms, but financially we had some questions.
"We have a counter proposal and will wait to see how Leverkusen reacts.
"We are not in a rush to sign. At worst, he plays another season in Amsterdam and leaves as a free agent after next season."