Roby, 27, limped off in Friday’s win over Wakefield, and coach Nathan Brown fears that his number nine could even be out for as long as 10 weeks.
Brown said: “Robes will be out for an extended period of time.
“We’re not sure how long at the moment as he is seeing a specialist on Tuesday. It is more than likely he will be out for a month and maybe as long as ten weeks. Ant Walker will be out for two to four weeks too.
“It is definitely something we didn’t want to happen but we will move on, move someone in there and that will give them the opportunity to do well for the team. I’m sure they will.”
Roby has played 26 or more Super League games in every season since 2005.