Ullrich sustained the injury during the Foals’ away fixture in Hamburg, with the 22-year-old left-back now set for an extended spell on the sidelines.
As a result, Ullrich will miss the upcoming international break with Germany U21s and will also be unavailable for Borussia over the coming weeks.
The injury represents a blow to Gladbach’s defensive options, with the club expected to be without the youngster for the next six to eight weeks as he begins his recovery.