Dortmund's Mario Goetze has suffered with muscular problems in recent months, prompting a comprehensive internal investigation into the possible causes, the club said on Monday.
Borussia Dortmund beat Hertha Berlin 3-2 on penalties to reach the German Cup quarter-finals on Wednesday after the match finished 1-1 after extra time.
Robert Lewandowski struck twice in the first half as holders Bayern Munich cruised past Schalke 04 3-0 on Wednesday to reach the German Cup semi-finals.