Reus will miss two weeks of action with a muscle strain, while Bender also picked up a knock in the 5-1 win over Werder Bremen.
The duo started the 5-1 Bundesliga win over Werder Bremen on Saturday, but were both withdrawn after 65 minutes.
The club said that Reus suffered a muscle tear, which will force him to miss games against Eintracht Frankfurt and Hamburg. Bender, meanwhile suffered a strain in his right thigh.
Dortmund, which had been struggling for form in the Bundesliga, thrashed Bremen at the Weserstadion thanks to two goals apiece from Robert Lewandowski and Henrikh Mkhitaryan and a Manuel Friedrich strike.