Lealiifano is on the verge of making an international comeback in the Wallabies' season-opener against South Africa almost exactly three years after being diagnosed with leukaemia.

He is competing with Bernard Foley and Matt Toomua for the Wallabies' chief playmaker role, but Larkham says Lealiifano's determination is sets him apart in the positional battle.

Lealiifano was told he may never play rugby again when his illness was diagnosed in August of 2016. He had chemotherapy and a bone-marrow transplant before restarting his Super Rugby career the following year.

"I knew what sort of character he was, I was 100 per cent positive he was going to get through it and play rugby again," Larkham said.

"I would say his fitness now is better than it's ever been. His work rate and his composure under pressure are better.

"One because of the ordeal he went through and the mental side of that, reassuring himself he was OK and ticking things off made him mentally stronger.

"I can see that composure in his game. Two because he's just fitter, you can see that as well.

"The real improvement I saw in the Brumbies game this year was the leadership on the ground and Christian was a huge part of that."

The Wallabies slumped to their worst season since 1958 last year, winning just four of 13 Tests to set off alarm bells before the World Cup in Japan this year.

MORE CANBERRA SPORT

The Brumbies could make up the bulk of the Wallabies side for the first Test given they were the only Australian team to play in the Super Rugby finals.

James Slipper could make his Test comeback after injury and controversy put his career on hold, while young gun Rob Valetini is fighting for a back-row spot.

Tom Banks is in contention to replace Israel Folau at fullback, but David Pocock's return from a calf injury will be delayed until the star flanker has fully recovered.

Lealiifano, who is in his first Wallabies squad since 2016, said he hoped a cohort of those from nation's capital would get a chance to shine.

"I think they [Wallabies coaches] are trying to use the strengths of [the Brumbies] and then add in their own twists and flavour on it as well," Lealiifano said.

"I think they've definitely acknowledged how well we've gone this year as a Brumbies team but just trying to maximise the strengths they use as well. The boys have done some mauling stuff and some scrum stuff and they're really adopting that to be on the same page."

Lealiifano is the new face to the playmaker mix for The Rugby Championship, but it is unclear if coach Michael Cheika will reward Super Rugby form or stick with combinations he knows.

There are just five Tests left before the opening World Cup game against Fiji on September 21.

Foley has played 68 Tests, with 54 of those since Cheika took the coaching reins at the end of 2014.

Lealiifano has played 19 Tests since making his debut in 2013 and will leave Australian rugby at the end of the year.

He struggled to maintain weight and be a physical presence in the early stages of his comeback, but he led the Brumbies to a semi-final this season and Larkham, who was the Wallabies' attack coach until this year, says he can be the glue for the Test back line.

But Lealiifano's statistics might convince Cheika he's worth a shot.

Lealiifano made double the amount of try assists than incumbent No. 10 Foley during the Super Rugby season, as well as making more line breaks.

"He has always had the attacking skills," Larkham said of Lealiifano. "But it was his defence that went to another level this year.

"I think the mental challenge of the life-threatening situation he's gone through means he's now pushing through pain thresholds and fatigue. You can see that towards the end of games, he played almost every minute of the season.

"He was on the field when games were won or lost for the Brumbies. He's worked really hard on his defence this year to get it back up and from a leadership perspective, he's an instrumental guy.

"I think that's something that has been lacking in the Wallabies, that's a massive strength he could bring to a team."