Bayern Munich's Javier Martinez may have torn his ACL, according to Sky Sports.
Martinez, 25, appeared in 18 matches last season in the Bundesliga, which the German club won by 19 points.
The Spanish international also appeared in one World Cup match this summer.
Martinez, who signed a multi-year contract with Bayern in August 2012, has played in the midfield and defense.
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Paul Breitner: We're sure Julian Green will be a great player for Bayern
Bayern Munich legend Paul Breitner thinks that Julian Green will be a great player and that he will stay with the club to reach that level.
- Chris Johnson