Hull KR prop Jonny Walker is expected to be sidelined for around eight weeks with a knee injury.
The 23-year-old limped off in the first half of the 30-10 defeat to Castleford on Friday, and scans have revealed he has damaged his medial colletaral ligament.
Walker has been struggling with a problem in his right knee, which has been heavily strapped throughout the early part of the Super League season.
But Rovers have confirmed the new injury is in his left knee, and he joins Dave Hodgson on the sidelines after the winger was also ruled out for two months with a similar problem.
Robins head coach Craig Sandercock said: "Jonny has damaged the MCL in his knee which is disappointing.
"It's not the knee that he's had trouble with in the past, it's his other one, and it looks as though he'll be having eight weeks on the sidelines."
Sandercock also revealed that Omari Caro is a doubt for this Friday's trip to St Helens after suffering a hand injury against the Tigers.
"Omari Caro also has a bit of an issue with his hand and he is a doubt for Friday. We'll have a look at him later in the week," Sandercock added.
But the Rovers boss had better news on Jamie Langley, Justin Poore and Mick Weyman, who have all been passed fit to return to the squad to face the Saints.
The trio missed last week's clash due to suspension and injury, and Sandercock added: "They're all raring to go and having three players of their experience available again is massive for us.
"We missed them last week and had a very inexperienced forward pack out there against Castleford which wasn't ideal."