Montgomery is absent from the lineup for Tuesday's game against Atlanta due to back tightness, James Fegan of SoxMachine.com reports.
It's unclear when the injury first surfaced for Montgomery, as he started the previous four games and is coming off a team day off Monday. The issue doesn't seem to be a serious concern, so the 24-year-old should be considered day-to-day for now. Luisangel Acuna is starting at shortstop Tuesday while top prospect Braden Montgomery was called up to make his MLB debut in the outfield.