Interest has been reported from Ajax, but were told to wait until the play off games were finished.
Ajax see Van der Hoorn as a replacement for Toby Alderweireld, who is likely to move in the summer abroad with many clubs interested in the belgium international.
Ajax face competition from PSV, but have the advantage of not having to sell players first. PSV may have to sell before they can buy new players according to media.
Ajax have had their scouts watch Van der Hoorn many times through the season and in the play off games.
Ajax also have Joël Veltman who is ready to step in, but with European games aswell competition for players is vital.