Dragons coach Anthony Griffin described Cameron McInnes's season-ending knee injury as "sad" and said trial form would be crucial to determining who takes his place.
Hours after McInnes went down with a ruptured ACL at training, curtailing his playing career in the Red V ahead of a move to Cronulla in 2022, St George Illawarra went down 36-28 to their outgoing captain's next club in an emerging players trial at PointsBet Stadium.
Only those who played 12 or fewer NRL matches in 2020 were eligible.
Speaking afterwards, Griffin acknowledged McInnes, who was touted to start at lock with the Dragons expected to sign Broncos hooker Andrew McCullough, is a tough man to replace.
"We've got a few there that can fill that [number 13] role," he said.
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"We'll have a look at it, see what fits us. Cam's a little unique because he can play hooker or lock. He plays well above his weight and can play 80 minutes as well.
"We've got two trials leading into the competition, so we'll see who puts their hand up. There's an opportunity there now. It's sad to lose him but there's an opportunity there."
Griffin didn't provide an update on McCullough's situation, saying "I think it's more up to the Broncos now rather than us as to when and if" he joins St George Illawarra.
However, McCullough's arrival on a three-year deal is expected to be confirmed by next week.
The likes of Blake Lawrie, Kaide Ellis, Poasa Faamausili, Trent Merrin and Jack Bird are among Griffin's options for the No.13 jersey.
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Ellis, along with fellow established NRL forwards Daniel Alvaro and Tariq Sims, was given around 20 minutes to shake off the rust against the Sharks.
"They'll get a better chance to push for a spot next week against Parramatta, we'll stretch their minutes out," Griffin said.
"It's disappointing for Cam and for the club but there's a spot there now that they can all zero in on. Everyone's disappointed but injuries are a part of the game. It's a brutal game sometimes, you can get a key injury like that."
St George Illawarra issued a statement on Friday afternoon to say McInnes would "undergo follow-up consultations to establish the next steps in his recovery and return-to-play timeframe."
McInnes's ACL tear also ensures Griffin will have to appoint a new captain, having put the decision off throughout the pre-season.
The 27-year-old's switch to the Sharks had already prompted the prospect of a change in leadership, and now the likes of Ben Hunt, Tariq Sims and youngster Zac Lomax head up the captaincy contenders.
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McInnes has played 91 games for the Dragons since arriving from South Sydney at the end of 2017, claiming St George Illawarra's best-and-fairest award for the past two seasons in underwhelming club campaigns.
His impressive form led to a call-up to the NSW Origin squad last year, with coach Brad Fittler singling him out for praise in camp despite not seeing any game time.
The fact St George Illawarra did not table an offer to McInnes during protracted negotiations, allowing Cronulla to swoop on his services, had sparked consternation among Red V fans and the NRL in general.