Bender twisted his ankle early in the second half and Turkey playmaker Sahin followed suit 10 minutes from time after clashing with an opponent.
"With Nuri it really does not look good. We have had easier moments. Now we need to wait on the medical results," coach Juergen Klopp, already missing several players, told reporters.
Dortmund are without central defenders Neven Subotic and Mats Hummels plus midfielder Ilkay Guendogan among others.
Last season's runners-up need to win their final Group F game away to already-eliminated Marseille on Wednesday to guarantee a place in the knockout stage.
Arsenal top the group on 12 points with Dortmund second on nine points, the same as Napoli.
(Reporting by Karolos Grohmann; Editing by Ken Ferris)
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