Heerenveen have decided not to extend the contract of defender Marcel Seip.
Seip has been at the club since signing in 2001 from BV Veendam and has played almost 100 games.
The 23-year-old has been unable to regain his place from Danish youngster Jakob Poulsen and will now leave the club at the end of the season.
Willem II have been linked with a Bosman move for the defender and Seip is thought to have already spoken with club officials.
Meanwhile, striker Lasse Schone has agreed a one-year deal with De Graafschap after Heerenveen failed to offer the 19-year-old an extension to his current contract.