Koller, his country's all-time record scorer with 55 goals in 91 appearances, quit the international scene in 2009 but continued to play club football and spent last season with French third-tier side Cannes.
He told his personal website: "Stopping my career was unexpectedly easy. I was prepared for a long time. I look forward to what lies ahead in the near future."
The 6ft 7in forward won the 2002 Bundesliga title during his five-year spell with Borussia Dortmund and also had stints with Sparta Prague, Lokeren, Anderlecht, Monaco, Nurnberg and Krylya Sovetov Samara.