Bradford defender Andrew Davies will be sidelined for up to two months after X-rays confirmed he has broken his arm.
Davies sustained the injury during a collision with Peterborough goalkeeper Jordan Pickford during Saturday's 1-0 home defeat and the 29-year-old will have surgery to repair damage to a displaced bone.
"It is clearly a blow to lose Andrew - he is probably fitter than he has even been at the moment," manager Phil Parkinson told the club's official website.
"He has had a great start to the season but we have the players within the squad to cope. We can't use this injury as an excuse.
"It is up to the player who comes into the side to replace Andrew to keep hold of the shirt now. We will regroup and come back strong."
Davies has endured rotten luck with injuries since joining Bradford, initially on loan, in 2011.
The former Middlesbrough, Southampton and Stoke centre-half missed three months of the Bantams' promotion-winning campaign during the 2012/13 season and was sidelined for 17 games last season following knee surgery.