Summary:
Borussia Dortmund's most-capped player is out of the Champions League after undergoing knee surgery.

Full article:
Borussia Dortmund playmaker Nuri Sahin will be out for an estimated two months after undergoing knee surgery on Wednesday, the Bundesliga club said. The 25-year-old Turkey midfielder, who returned to Dortmund in 2013 following unsuccessful spells at Liverpool and Real Madrid, had inflamed tissue removed from his left knee. Sahin signed for Liverpool on loan in the summer of 2012 but failed to establish himself, making just 12 appearances and has since returned to Dortmund for a second spell at the Bundesliga club. Ruled out: The playmaker will miss the Champions League group stage clash against Arsenal on September 16 . 'Borussia Dortmund team doctor Markus Braun expects his recovery period to last about two months,' Dortmund said in a statement. Dortmund, last season's league runners-up, are also competing in the Champions League Group D along with Arsenal, Galatasaray and Anderlecht. The German-born Sahin joins several other Dortmund players, such as Ilkay Guendogan, who has not played since last year, Jakub Blaszczykowski and Marcel Schmelzer on the sidelines. Tough spell: Sahin endured a disappointing loan move to Anfield before re-signing at Borussia Dortmund .