Borussia Dortmund midfielder Nuri Sahin underwent knee surgery on Wednesday and will be out for around two months.
The Turkey international was initially ruled out for three weeks after it was revealed he suffered tendon damage in training.
However, Sahin is now set for a longer spell on the sidelines after undergoing an operation on his left knee.
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A statement on the club's official website said: "Nuri Sahin has had surgery on Wednesday in the Isar Clinic in Platt Park Ling.
"Dr. Heinz-Jurgen Eichhorn removed inflamed tissue from Sahin's left knee during surgery. Borussia Dortmund team doctor Markus Braun based an approximately two-month rehabilitation period for the Turkish national player."
Dortmund coach Jurgen Klopp has had to contend with a lengthy injury list at the start of the season, with Jakub Blaszczykowski and Ilkay Gundogan among his other absentees.