The midfielder was initially thought to have torn a calf muscle until a new diagnosis was made on Monday afternoon. He is expected to miss the remainder of the season.
Bayer Leverkusen midfielder Kevin Kampl is expected to miss the rest of the season after being diagnosed with a broken leg.
The 25-year-old Kampl came off the pitch injured in last Sunday's match against Borussia Dortmund and was initially thought to have torn a calf muscle.
However, a fresh scan conducted in Cologne on Monday found that he had actually broken his left fibula in a tackle that forced him out of the Bundesliga match.
The Slovenian international has been one of coach Roger Schmidt's stand out performers this season, with two goals and five assists for Leverkusen.
Kampl joined Leverkusen from Dortmund in the 2015 January transfer window, and has become a first-team regular at the Rhineland club.