Bender, who broke facial bones in two injuries last season, was elbowed in the face and taken off after 63 minutes of Wednesday's game.
"It is confirmed that Bender broke his nose," the club said in a statement on Thursday after conducting further tests on the player. "The team doctor has ruled he can play against Mainz."
"Maybe [Sebastian] Kehl's mask fits Manni [Bender]," joked coach Klopp earlier in the day.
Dortmund captain Kehl also broke his nose earlier this season and played with a face mask.
The German champions, who advanced to the Champions League knockout stage, are nine points behind leaders Bayern Munich in the Bundesliga in fourth place.
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