Hummels suffered a sprained ankle during a friendly match against Fortuna Dusseldorf on Tuesday morning and is now set for another spell on the sidelines.
The 25-year-old had only just returned from a two-month injury layoff with torn ligaments, although his latest setback is not related to that problem.
Hummels helped his side to a 2-1 win over Eintracht Braunschweig on Saturday in his first match back since being forced off during Germany's friendly win over England in November.
However, he will now miss Bundesliga matches against Werder Bremen and Eintracht Frankfurt, as well as a DFB-Pokal clash with Frankfurt next week.
The German international is expected to return in time for the Champions League last-16 match against Zenit St Petersburg on February 25.