Dortmund playmaker Sahin out for rest of season
The 22-year-old Turkey international, who has been outstanding this season, was injured in their win over Freiburg on Sunday.
"He will not be able to compete this season again," said club doctor Markus Braun on their website.
Sahin, who has been linked with a move to Real Madrid in the close season, will be out for an estimated six weeks.
Dortmund, who lead the standings by eight points with four games left, could clinch the title this weekend if they win and rivals Bayer Leverkusen draw or lose their game.