Super League leaders St Helens will be without captain James Roby for a month as he prepares to undergo groin surgery.
Saints coach Justin Holbrook says the England hooker has been affected by the injury for several weeks.
"Robes has been struggling with it for a while," Holbrook said after his side's shock 23-22 defeat by bottom club London Broncos.
"He'll get some minor surgery this week so he'll probably miss four weeks."
Understudy Aaron Smith will deputise in Roby's absence, starting with the visit of Huddersfield on Friday, but the skipper is expected back well before his club's Coral Challenge Cup semi-final against Halifax on July 27.