St George Illawarra chief executive Peter Doust says the joint venture will not be splashing out on a big-name signing to replace the retiring Mark Gasnier next season.

Gasnier announced on Thursday he will quit the NRL at the end of the season despite having three years remaining on his contract.

The NSW centre, who is the nephew of Dragons great Reg Gasnier, admitted he could not commit himself to another season and felt it was only fair to the Dragons to quit, despite not turning 30 until next week.

"I decided earlier on in the year, it was just finding the right time to announce it, that is always difficult but it is post-Origin and pre-finals so it's a good time," Gasnier told a packed press conference at Kogarah Oval.

"It was something I'd considered for a long time, it suits everyone involved with the decision, I can move on with the next stage of my life and the club can move on."

Doust tried to talk Gasnier, who returned to the club from French rugby last year to help them win their first grand final since becoming a joint venture, out of quitting but conceded he knew he wouldn't have succeeded.

He said the centre would be missed but the club won't be looking outside its own ranks for a replacement.

"When you plan forward for rosters in the go-forward sense you have to know these things pretty early in the piece," Doust said.

"You make decisions about coaches, you make decisions about players.

"We are not out chasing an outside back as such, Kyle Stanley ... he is an important long-term part of our future.

"Jason Nightingale is the same and we have added Tim Moltzen to our roster as well and Chase Stanley is coming back as well so there is nobody big out there that we are after."

Gasnier played 15 Tests for Australia between 2001 and 2008 as well as 12 State of Origin matches for NSW, including the most recent series, but revealed he'd not told Blues coach Ricky Stuart of his decision ahead of last week's clash with Queensland.

He also said injuries were not a factor, but admitted he would not have had the hunger to play on in 2012 and his decision had nothing to do with Wayne Bennett's departure to Newcastle next year.

"Physically I could play on for a couple of years, but mentally I couldn't," he said.

"I would love to be coached by Steve Price and it didn't have one ounce of influence on my decision that Wayne was going and he was coming in.

"To be on good money you need to be 100 per cent committed and mentally I don't think I could do that. This decision suits everyone.

"I think it is the right thing to do for me and the club."

Gasnier said he's undecided about his future but laughed off a question if he would return to rugby and dismissed any notion of following Bennett into coaching.

"I've got no interest in coaching, it has to be the hardest job in the world," he said.

"If it was helping outside backs on an individual (basis) that would be interesting, I love working with individuals.

"But as far as being a full-time coach, that is not for me."

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