Duff, recently back from an Achilles injury, was forced off in last weekend's home defeat to Barnet after sustaining a knock to the lower back.
The Bantams are already without fellow centre-half Steve Williams, who is still struggling with a hamstring injury, so Rob Kiernan, on loan from Watford, could return to the starting line-up alongside Luke Oliver.
Midfielder Tom Adeyemi, on loan from Norwich, did not appear for the second half against Barnet due to an on-going ankle problem, but is expected to be fit.
Striker Jake Speight, back from his loan spell at Port Vale, scored for the reserves in midweek and will be in contention but Mark Cullen, the new loan signing from Hull, is hoping to start up front after stepping off the bench last week.
Source: PA
Source: PA