Sean Scannell has been ruled out for at least three months.
Tests have revealed the midfielder, who joined the Bantams in July, has sustained a stress fracture in his back.
Scannell will visit a spinal specialist next week to reveal the full extent of the injury, which is likely to keep him sidelined until at least the end of January.
Meanwhile, midfielders Jim O’Brien, Jordan Gibson and Danny Devine returned to full training earlier this week, alongside striker Tom Clare.
Ben Wilson (knee), Joe Riley (quad), Luca Colville (knee) and Alex Jones (hamstring) are expected to return to full training within the next two weeks.
Kelvin Mellor, who suffered a broken toe during City’s defeat to Rochdale, will be back in contention before the end of this month.
Cameron Hawkes (knee), Jake Reeves (pelvis) and Curtis Peters (foot) remain sidelined.