St George Illawarra have suffered a significant body blow ahead of their vital NRL match against Manly, with fullback Josh Dugan ruled out due to a hamstring injury.

Dugan pulled up sore from last week's golden-point loss to Canberra however, at this stage, the Dragons are hoping the injury is only minor.

"Upon follow-up scans, it was determined that he would miss this weekend's game against Manly," performance manager Nathan Pickworth said.

"He will be reviewed and progressed accordingly over the next couple of days."

It caps off a difficult week for the NSW State of Origin centre, who has been the focus of the fallout from the Blues' series-decider loss after he and Blake Ferguson's six-hour visit to a pub on a day off.

It represents a massive hit to the Dragons' top-eight hopes.

St George Illawarra are hanging on by a thread to their spot in the eight, having dropped seven of their past 10 games.

Jason Nightingale will return to fullback - a position he has played regularly this year - while Matt Dufty is set to make his NRL debut off the bench as Kurt Mann goes to the wing.

In better news for the Dragons, Russell Packer is set to overcome a hip injury to play, while Tyson Frizell is also considered certain to return from a hip injury.

Blake Lawrie, after playing NSW Cup on Saturday for Illawarra, will drop off the bench, along with Taane Milne.

The injury news came after coach Paul McGregor believed he had seen the Dragons turn a corner in last week's loss.

"We know where we are on the ladder," McGregor said.

"It wasn't a complete performance but it was a clear sign of improvement on previous weeks.

"We created three good scoring opportunities last week. We played direct, we played more straight and we engaged the line better.

"We do need to execute our finishes a little bit more. The line speed was more consistent last week.

"We need to build on that performance."

Manly also have injury worries, with boom hooker Apisai Koroisau ruled out with a calf injury.

They will also rely on a secondary goal-kicker, with winger Matthew Wright succumbing to a hip issue.

STATS THAT MATTER:

* The Dragons scored at least 16 points in their first seven rounds, but have done so just four times since

* The Dragons' left edge is the most-dominant in the NRL, with 31 tries this year

* Manly lead for points per game (23.3)