Already riding high at the top of the NRL ladder, St George Illawarra will on Sunday unleash the secret weapon they hope will convert their regular season success into an NRL premiership.

Former Warriors half-back Nathan Fien will make his Dragons debut when he comes off the bench against Manly at WIN Stadium. The New Zealand Test representative is shaping as an intriguing x-factor after being snapped up just before the June 30 deadline when let go by the Warriors.

The Dragons have been running like a well-oiled machine so far in 2009, but the addition of Fien - a current international - represents a major upgrade to their bench strength with local junior Mathew Head set to make way.

"He has played nearly 200 NRL games. He's a great pick-up for us and an addition to our side that we think can help us," Dragons skipper Ben Hornby said.

"He'll play as hooker. He has been doing most of his (training) at hooker so we expect him to come on and give us a lift there."

Both sides have been decimated by injury and Origin commitments, with Manly star Jamie Lyon an almost certain non-starter despite threats from Sea Eagles management that the former Test centre would line up for the visitors after being ruled out of the third State of Origin match with an ankle injury.

Manly will have the services of Test prop Brent Kite however after he was dropped by Blues selectors. The former Dragon is no doubt keen to answer his critics with a strong performance.

That's the last thing rookie Dragons prop Trent Merrin would want to hear, with the 19-year-old still finding his feet in the top grade.

Merrin had an inauspicious start to his NRL career when he was left on the bench for the entire 80 minutes by coach Wayne Bennett in what was set to be his debut game against Brisbane in round four.

Bennett sent him back to the NSW Cup with Shellharbour but he has since gone on to play two matches in the NRL. Merrin says the experience against the Broncos had proved fruitful even without any onfield action.

"To even be a part of the team was a dream come true," Merrin said.

"Just sitting on the bench, it was a good eye-opener, just to see how the game panned out.

"When I sat there I didn't think I was up to it. It helped me out a lot.

"He (Bennett) just came up to me and said it wasn't the right time to put me on. You'll get your chance so just hang in there."

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