The Turkey international, who joined Dortmund on a permanent basis from Real Madrid CF earlier this year, left BVB's Bad Ragaz training camp for Munich on Thursday to undergo tests on the injury, which revealed the extent of the damage. Sahin now faces a race to be fit for the start of the Bundesliga season.
Mainstay in midfield
The injury has been a considerable source of frustration for the 25-year-old who, despite playing 45 minutes of die Scharz-Gelben's 5-0 victory over Rot-Weiss Essen on Sunday, has been forced to take things easy during pre-season training thus far.
An ever-present for Dortmund in the Bundesliga last season, Sahin scored twice and chipped in with three assists as Jürgen Klopp's side finished runners-up to FC Bayern München in Germany's top flight. He also played in every minute of BVB's UEFA Champions League campaign up until their quarter-final second-leg against former employers Real at Signal Iduna Park.