Callahan sustained a lower-body injury in Tuesday's game versus the Red Wings and won't return, Joe Haggerty of Boston Sports Journal reports.
Callahan was missing from the bench during the second period, and this would explain why. The 26-year-old's injury adds to a growing list of unavailable blueliners for the Bruins -- Callahan himself was called up when Henri Jokiharju (undisclosed) landed on injured reserve. Another roster move may be incoming if Callahan can't play Thursday versus the Blues.