St George Illawarra have been tested by State of Origin commitments before, but skipper Ben Hornby claims the representative season has never had a bigger impact than the one threatening to derail the club's NRL premiership defence.

The Dragons depth will be tested yet again on Friday night when the ladder-leaders go up against Brisbane without their starting backrow, with Ben Creagh and Beau Scott failing to back up from NSW's Origin II win on Wednesday night.

Creagh suffered an ankle injury and Scott a medial ligament strain and perforated eardrum in a double blow which could see the pair sidelined for 2-3 weeks, putting their participation in the Origin decider in some doubt.

It has also put a strain on the Dragons' depth - even more, according to Hornby, than it did in the early 2000s when the likes of Mark Gasnier, Matt Cooper, Jason Ryles, Luke Bailey, Trent Barrett and Shaun Timmins were Origin regulars.

"I think this is the most we've had to deal with at the Dragons - obviously we've had four or five (in the past) and you can sort of deal with that, but on top of the injuries we've copped in the last couple of weeks, it has been pretty tough," Hornby said.

Joining Creagh and Scott on the sidelines are Cooper (fractured cheekbone) and Brett Morris, who was a late withdrawal from the side to face the Broncos, with Ratu Peni Tagive to come into the side.

The Dragons' once-healthy buffer at the top of the ladder is down to just one point as Manly and Melbourne close in, after a draw against Parramatta was followed by last week's loss to Gold Coast - just their second this season.

With games against Manly and Newcastle to follow Friday night's trip north to face the Broncos before the Dragons get their second bye, Hornby said the club just had to do the best it could over the next few weeks.

"It's a tough period but at the moment they're the cards we're dealt, we've got to try and overcome it," Hornby said.

"It's hard to get any sort of rhythm to your game, that's the biggest problem.

"You build up the first half of the season getting your combinations and for the middle part of the year it's all out the window."

The Dragons refused to reveal who would come into the side for Creagh and Scott, but it is believed Adam Cuthbertson will come off the bench to take one vacancy with the likelihood that Dean Young will shuffle from hooker to join him.

That would see Nathan Fien elevated to a starting role at hooker, with young sensation Alex McKinnon, Michael Greenfield and Jack Bosden fighting it out for the two vacancies on the bench.

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