Canberra lock Shaun Fensom has been ruled out of the NRL for up to six weeks after sustaining ligament damage to his thumb against the Roosters on Saturday.
Fensom underwent surgery on Tuesday afternoon, leaving the ninth-placed Raiders without their key defender for the remainder of the regular NRL season.
Joel Edwards has been named as his replacement.
"I was hoping I could play with the injury and get through the year before having surgery at the end of the season," Fensom said.
"Unfortunately the risk of permanent damage was too great so I have to get it done now."
On the plus side, Raiders captain Terry Campese has been provisionally named to play the Bulldogs at Canberra Stadium this Saturday despite being accidentally struck in the eye by teammate David Shillington in the match against the Roosters.
Campese will be assessed again later in the week, leaving the Raiders to sweat over his fitness.
His possible replacement Sam Williams has only just commenced rehabilitation running on his injured ankle, while young-gun fullback Anthony Milford would face a massive challenge in his debut NRL season spearheading the Raiders' attack.
Meanwhile, representative forward Tom Learoyd-Lahrs will test out the strength of foot ligaments he tore against the Melbourne Storm in round eight at training throughout the week.
Despite not being named in the Raiders' 18-man squad on Tuesday, Learoyd-Lahrs was optimistic his 12-match stint on the sidelines had drawn to a close.
"The injury is about as strong as it's going to get so I've just got to get the confidence in training," the 27-year-old said.
The Raiders have fallen out of the top eight to ninth place after back-to-back losses to competition favourites the Storm and the Roosters.
Their remaining four matches include three other top six sides and an away trip against fellow top eight contenders the Warriors.
"I'm hoping to inject a bit of enthusiasm and bit of energy to the side when I get back to make up for a bit of lost time," Learoyd-Lahrs said.
Winger Edrick Lee has also returned to squad training from his broken arm, but is still expected to miss another two to three weeks.
Raiders: Anthony Milford, Sandor Earl, Jarrod Croker, Blake Ferguson, Jack Wighton, Terry Campese, Josh McCrone, David Shillington, Glen Buttriss, Dane Tilse, Josh Papalii, Joel Thompson, Joel Edwards. Interchange: Shaun Berrigan, Jake Foster, Brett White, Paul Vaughan, Reece Robinson (18th man).
