But assistant coach Dan McKellar has backed a "changing of the guard" in the Brumbies squad to maintain high standards despite losing the experience of 242 Test and 615 Super Rugby games for next year.

The departure of Robbie Coleman and Christian Lealiifano's fight against leukaemia is set to open two contract spots for the Brumbies to fill.

The duo's absence, combined with Matt Toomua's move to England, leaves the Brumbies without an established flyhalf or inside centre, although Kyle Godwin is in line to fill the No. 12 jersey.

Tuggeranong Vikings star Isaac Thompson will join the Brumbies for pre-season training while the club will also look at playmakers around the world to see if they can add experience to their roster.

Wallabies veteran and former Brumbies captain Matt Giteau looms as an ideal candidate, but the 34-year-old is one of the highest-paid players in the world and has a contract with French glamour club Toulon.

Lealiifano will take on a coaching role if he is unable to play next season and he will start his next phase of treatment in Melbourne at the end of the week, including a bone-marrow transplant.

McKellar, who will take over head coaching duties while Stephen Larkham is with the Wallabies, said the Brumbies had faith in young guns Jordan Jackson-Hope, Nick Jooste and Godwin.

But he conceded there was room for another chief playmaker in their roster as they aim for a fifth consecutive finals berth and a Super Rugby title.

"The way rugby is these days, guys look for new challenges overseas or in Australia as well," McKellar said.

"We're comfortable with where we sit as a squad but we do have a couple of holes to fill there.

"With Robbie leaving there is a contract up for grabs and depending on Christian's situation as well, we'll wait to see how he goes with his treatment.

"The reality is that we'll probably need someone for Christian next year. There are some good guys around, so we'll have a look in New Zealand and Japan, as well as here, to give someone a crack."

Coleman joined the list of Brumbies departures on Friday after finalising a deal to move to the Western Force, while Canberra junior and Australian sevens star Tom Cusack has signed a Super Rugby deal with the ACT.

Coleman, Lealiifano, Toomua, David Pocock, Stephen Moore and Josepth Tomane will all be absent from Brumbies duties next year, leaving a massive hole of experience in the squad.

The Brumbies were forced into a rebuilding period in 2012 when they started a new generation with just three Wallabies players in their squad.

The similarities are starting to appear, with just three 2017-contracted Brumbies players – Scott Sio, Rory Arnold and Henry Speight – starting in the Bledisloe Cup Test against New Zealand on Saturday.

Players including Jarrad Butler, Sio, Scott Fardy and Sam Carter will be called on to step up as leaders to help usher in a the next era of players.

The Brumbies have been touted as Australian conference favourites in recent years, but McKellar says their new-look roster could mean they fly under the radar.

"There's a changing of the guard but that's exciting," McKellar said. "It's an opportunity for other players to step up and I think we've recruited well to fill some gaps.

"You mention the guys we've lost but there's Kyle Godwin coming in and Chris Alcock, who I think is a very under-rated footballer.

"We've got Lolo Fakasoliea as well. We're losing some players, but we're comfortable with the quality of people we've brought in.

"We're excited that potentially we may fly under the radar and just go about our business in Canberra. In the past, that has always worked well for the Brumbies."

The Brumbies have gone their separate ways for an off-season holiday before returning for pre-season training on November 17.

McKellar and Peter Ryan will lead the Brumbies while Larkham is with the Wallabies as an assistant for their end-of-year tour to Europe.