St George Illawarra prop Paul Vaughan.

St George Illawarra's premiership campaign has been dealt a savage blow, with Paul Vaughan ruled out for the rest of the season after suffering a foot injury at training on Tuesday as he attempted to return for Jason Nightingale's farewell home match.

Vaughan took part in a full training session on Tuesday for the first time since injuring his ankle in the round-21 loss to the Warriors but the NSW Origin prop was hobbling badly by the end of the workout and was later fitted with a moonboot.

After receiving the results of scans on Vaughan's left foot, St George Illawarra Head of Athletic Performance Nathan Pickworth said that the new injury had ended his 2018 season.

"Paul suffered a season-ending injury to his foot in a freak incident at training," Pickworth told Dragons.com.au. "Paul's foot injury occurred on the opposite leg to the one he previously suffered against the New Zealand Warriors in Round 21."

It is believed Vaughan suffered the injury after getting his foot caught in a tackle with a team-mate. The 27-year-old said he was gutted to be ruled out for the remainder of the season.

"I'm devastated that my season has come to an end so suddenly today," Vaughan said. "However, I'll continue to support the boys for the rest of the year, and I look forward to coming back bigger and better in 2019."

Vaughan had been named in an extended 21-man squad for Sunday's clash with Canterbury but the return of Nightingale, whose wife Bianka gave birth to their second child on Tuesday, from a neck injury will be the only change from the team which beat Wests Tigers last weekend.

The Dragons are also without injured captain Garetth Widdop after he dislocated his shoulder in the round 22 loss to Parramatta but his replacement Kurt Mann revealed the English five-eighth may play next weekend against Newcastle.

"I think they are playing it week by week at the moment," Mann said of Widdop’s return. "They have tossed up maybe next week the way he has been going but it could be the week after as well - the first week of finals.

"He is so crucial to what we do, he is our skipper and we need him towards the back end of the year."

Test forward Tyson Frizell has been playing in the middle in Vaughan's absence, with Luciano Leilua starting as the left edge back-rower.

It is a role Frizell is familiar with as he usually starts on the right edge for NSW and Australia and moves into the middle later in the match to enable another second-rower to come off the bench.

"I am happy playing that position if that is what our team needs," Frizell said. "I have done it in the past, I have done it in Origin and I have done it for Australia so it's not something too unfamiliar for me.

"A couple of years ago I was playing the same sort of role, playing on an edge and then coming into the middle. It is more like a third back-rower playing in the middle of the field. I am not the same size as some of the props these days."

After losing five of their previous six matches, Frizell said there was a feeling within the Dragons camp that last Saturday’s 20-10 win over the Tigers was a turning point for the team in getting their season back on track ahead of the finals.

As they had done in previous losses to the Tigers, Warriors and Eels, the Dragons failed to capitalise on early chances, conceded a large number of penalties and had a player sent to the sin bin but they rallied after losing halfback Ben Hunt for 10 minutes to grind out a gutsy win.

"It definitely felt like the team we have been throughout the start of the year," Frizell said. "There was a feeling at stages of the game in the past couple of weeks where we have been lost when that adversity had come our way.

"We have still got a long way to go in terms of being the team we know we can be but that was a step in the right direction. In the past few weeks we would have dropped off and let teams roll us but that feeling was back and our defensive effort was on point. We are going to need that in the finals."