Barnsley have allowed goalkeeper Heinz Muller to join Bundesliga side Mainz in a £600,000 deal.
Muller joined the Tykes from Lillestrom two years ago for £150,000 and made 69 appearances during his time with the South Yorkshire club.
The German keeper struggled to reclaim his starting place after suffering a cruciate knee ligament injury in January 2008 and finished the season as back-up to former understudy Luke Steele.
"Heinz has been given the opportunity to play in the German top-flight and it was the right deal for Barnsley Football Club," manager Simon Davey told the club's official website.
"It is a good deal for both the club and for the player and we wish him well in the future."