Goulburn junior Lachlan Croker will never forget his debut NRL match.

The pain of a reaggravated shoulder injury - which forced the youngster from the GIO Stadium turf moments before halftime on Saturday - was soothed by the Canberra Raiders' unlikely 21-20 victory over the Sydney Roosters.

The Goulburn Bulldogs product showed positive signs in his quest to temporarily fill the vacancy left by Raiders' talisman Blake Austin.

The positive signs might be in vain, however.

Raiders medical staff will today determine the severity of Croker's shoulder injury - sustained during an attempted tackle on Aidan Guerra.

The 19-year-old last year had surgery on that very shoulder.

During his 38 minutes on centre stage, Croker showed glimpses of potential. A crafty offload to namesake Jarrod Croker tested the Roosters' right side defence, while a spiralling bomb challenged opposition fullback Latrell Mitchell.

Conversely, a fumble in his side's 10 metre zone helped the Roosters open up a 16-6 halftime lead while an opening set defensive penalty gave the visitors momentum.

If the feedback from Fox Sports sideline commentator Nathan Fien is any guide, Croker is in serious doubt for the Raiders' round three match with Newcastle.

"Lachlan Croker, on debut, has re-injured that shoulder," Fien reported during the game's coverage.

"The Raiders medical staff are being coy, saying he could come back on if he has to."

That moment never arrived.

Despite little possession, a mounting penalty count, injuries to both debutant Croker and hardworking backrower Shaun Fensom, and a scoreboard deficit, the Raiders rallied.

Captain Jarrod Croker, also a celebrated Goulburn junior, proved influential in that comeback.

The senior of the two Goulburn Crokers laid on Canberra's second try and scored and converted another to square the match at 20-apiece.

A late field from halfback Sam Williams ensured that Lachlan Croker's NRL debut ended in triumph.

That victory isn't a cure for Croker's pained shoulder. Raiders coach Ricky Stuart is hoping his charger can recover in time to take on Newcastle.

The man himself is confident he'll be fit for kick-off and poised for improvement with the benefit of a game's experience.

"Obviously it's good to get the win, but it's different sitting on the bench and knowing you weren't out there playing your part," Croker said after Saturday's match.

"But I'm stoked for the boys and stoked to win my first game, so nothing will dampen that."

In the meantime, Canberra remains without the services of first choice halves Aidan Sezer and Blake Austin.

The injured pair won't return until at least round five, opening the door to more NRL games for the up-and-coming playmaker.