The hard-nosed former Brisbane Broncos and Brumbies forward is leaving Canberra after four years of building and maintaining one of the best defensive units in Super Rugby.

Ryan's departure will be a blow to the Brumbies' brainstrust, but he is likely to be one of only a handful of changes as coach Dan McKellar weighs up whether to recruit another mentor.

The dual code premiership-winner considered leaving at the end of last year, but made a commitment to McKellar to stay for one more season to help the head coaching transition.

"I thought Dan deserved to have a bit of continuity coming into this year, but in reality my mind was made up that this would be my last season at the Brumbies," Ryan said.

"I'm happy with my decision. I'm glad to be coming home [to the Sunshine Coast] and having a lot more time with my wife and kids."

McKellar has already turned his attention to recruiting players to add to his squad for next year, but there are only a handful of spots up for grabs despite the Brumbies losing 10 players.

The squad size was inflated to 39 this year, but that will be cut back to 36 and McKellar has started negotiations to find replacements.

Ryan and physiotherapist Byron Field, who is joining English club Bath, are two of the changes in the back-room staff.

Ryan has helped the Brumbies be one of the best defensive teams in his four seasons, leaking the fewest points of any team in 2014 and the third least in 2017.

"He's a good man, Ryno. He brought that rugby league mentality and hard edge to our game," McKellar said.

"He's been an integral part of our group and we'll miss him. He's spent four years down here, been living away from his family for that period and he wants to get back home.

"I've always been heavily involved with the defence side of things, have worked closely with Ryno. It would be unlikely we'd bring another coach in on a full-time process."

Ryan has already been contacted about consultant coaching work, such is the respect for what he does in the collision and tackling technique area of the game.

He has long held a desire to break into the United States market and transform the way NFL franchises approach tackling to make them efficient in defence.

He has previously visited Super Bowl champions the Denver Broncos and New York Giants and hopes to build a relationship in the US to work with teams.

The Broncos premiership winner and Super Rugby champion is also part of the Fiji coaching set up for the World Cup in Japan.

"Fiji is really untapped and I think the ability for them to do well in the World Cup is there for them to take," Ryan said.

"The US and the NFL is an untapped resource there as well because of the work and the scope. There is 350 million people there, a high percentage of people who play American football and I think for the betterment of their sport, high quality contact through tackle technique would improve it."

BRUMBIES SQUAD UPDATE

DEPARTING PLAYERS: Kyle Godwin, Isi Naisarani, Richie Arnold, Nic Mayhew, Andrew Smith, Lolo Fakaosilea, James Dargaville, Mees Erasmus, Faalelei Sione, Michael Oakman-Hunt.

YET TO RE-SIGN: Christian Lealiifano, Ben Alexander, Ben Hyne, James Verity-Am, Connal McInerney, Robbie Abel.

CONFIRMED RECRUITS: Pete Samu.