Müller started his first-team career with the German amateur club FSV Frankfurt in the summer of 1996 and went on to then Regionalliga Nord side Hannover 96 after one season.
He transferred to Norwegian club Odd Grenland in the summer of 2004 and played there until the end of the year before moving to Lillestrøm in January 2005.
In August 2007, Müller moved to Barnsley[1] on a three-year contract and made a number of superb performances.
A highlight in his debut season was saving an Andy Keogh penalty in a 1–0 win over Wolverhampton Wanderers in December 2007.
[2] In January 2008, Müller suffered a horrific injury to the lateral meniscus whilst playing against Colchester United.