Stuart was standing close by and was one of many who head the 'snap' that ended Priest's season when he slipped at a Canberra Stadium training session on Wednesday night.

It has thrown down another injury speedhump to the Raiders but Stuart has backed club depth to stand tall when Canberra needs it most.

Former Melbourne forward Jeff Lima looms as the likely man to step up, while Stuart also has the chance to turn to Mal Meninga medallist Shaun Fensom or Paul Vaughan for a must-win clash against the Penrith Panthers.

Friday looms as a decision day for Stuart as he weighs up who will replace Priest on the bench and checks on the fitness of injured duo Blake Austin (hand) and Josh Hodgson (ankle) for the do-or-die final.

NRL rookie Priest was ruled out for the rest of the year, opening the door for Jeff Lima, Fensom or Vaughan to charge back into finals contention.

Penrith junior Austin got through his first test on Wednesday night, but it's understood medical staff want to see him get through another session with his repaired broken hand to see if it's ready to handle the NRL workload.

Hooker Hodgson hoped to run at the team's final training session on Friday to test his ankle ligament damage.

Either way Stuart will turn to the club's much-vaunted depth to fill the void left by Priest.

The Raiders' depth has been a major driving force in their on-field revival, with Stuart able to shake up his line-up and throw experienced players back into the NRL when needed.

Lima looms as one of the front-runners to replace Priest given his NRL finals experience, but hasn't played in first grade since injuring his hip in May.

"It's shattering for Clay, he's had a great year. We heard the snap and knew it was bad, but we're fortunate in a way because we do have players there who can come in when needed," Stuart said.

"It makes it hard on players but competing for spots has been a big part of our theme this year. This is where it becomes an advantage for our squad because we can bring in a first-grade player [for Priest]."

Stuart was close by when Priest's season came to a shattering and unexpected halt and heard the snap as the bench forward went down in pain.

The 27-year-old was a rugby league unknown at the start of the year and spent most of his time fixing powerlines in Sydney.

But he was plucked from obscurity in April and played 14 games in his rookie season to earn a two-year contract upgrade.

"For a guy to miss out on such a big game and the exciting part of the season, it's disappointing for him," Stuart said of Priest.

"It was disheartening to see it happen and we knew what the situation was straight away. It was a bad injury.

"He's a tough kid and he's going to be a big part of us going forward. He's a late developer and a really good model for young blokes who don't make it at 19, 20, 21 years old.

"He showed if you keep working hard and sacrificing, you'll get your crack. He hasn't looked back."

Fensom, Lima and Vaughan have been waiting for a chance to make their mark on the finals.

Lima has battled injuries this year and has played just six games while Fensom has been forced to bide his time in reserve grade.

Priest started the year in the NSW Cup before impressing Stuart to earn his shot at the big time.

"Just to play one game of NRL is amazing, so to have this journey is an added bonus," Priest said on Tuesday.

NRL SEMI-FINAL

Saturday: Canberra Raiders v Penrith Panthers at Canberra Stadium, 7.40pm. Tickets available from Ticketek.

Raiders team: 1. Jack Wighton, 2. Edrick Lee, 3. Jarrod Croker, 4. Joey Leilua, 5. Jordan Rapana, 6. Blake Austin, 7. Aidan Sezer, 8. Junior Paulo, 9. Josh Hodgson, 10. Shannon Boyd, 11. Josh Papalii, 12. Elliott Whitehead, 13. Sia Soliola. Interchange: 14. Kurt Baptiste, 15. Luke Bateman, 17. Joe Tapine, one to be added.