The center back picked up the injury in Germany's 1-0 international friendly win over England on Tuesday and underwent a series of tests on Wednesday to determine the extent of the knock.
Dortmund initially hoped that the injury would not be too serious, but the 24-year-old has now been diagnosed with a fractured metatarsal that will keep him out of action until halfway through January.
Hummels will consequently miss this weekend's Bundesliga match against Bayern Munich as well as the Champions League games at home versus Napoli and away against Olympique de Marseille.
Furthermore, Marcel Schmelzer will be unavailable for three weeks after picking up a calf problem while away on international duty with Germany as well.
The left back will definitely miss the matches versus Bayern and Napoli, but could be match fit again in time for the clash with Marseille on December 11.
Dortmund was already without the injured Ilkay Gundogan and Neven Subotic for this weekend's match at the Signal Iduna Park.