Bradford captain Robbie Paul broke his right arm during the Super League defeat by St Helens and will miss up to eight weeks of the season. The New Zealand international suffered a double fracture after falling awkwardly midway through the second half at Odsal.
The 27-year-old will have surgery on Saturday.
The injury completed a miserable night for the Bulls, who were beaten 35-0 by their Super League rivals. "Obviously it is very disappointing to have lost him," said Bulls coach Brian Noble.
"He has been playing really well for us this season. We will miss him."
Paul's injury rules him out of New Zealand's Test match against Australia on 25 July.