Mayhew will be a contender to fill Sio's loosehead prop spot with the Wallabies front-rower facing another stint on the sideline.

Sio returned to Canberra in a brace after his knee twisted awkwardly in the first scrum of the game against the Wellington Hurricanes on Friday night.

It was a cruel blow to Sio, who missed the first month of the season with a hamstring problem, and compounded a 56-21 thumping by the Hurricanes.

The Brumbies' scrum has wobbled at times in the past two weeks under different referee interpretations.

But Mayhew stood tall under pressure when he he was thrown on to the field after just 11 minutes and could be set to start against the Blues next weekend.

Mayhew, 28, played 11 games for the Blues in 2015 and 2016 before moving his career to Canberra this year.

"Nic certainly did a good job when he came on and he was involved heavily in the first try to create a line break," Larkham said.

"We just have to wait and see with [Sio], it didn't look good and he's in a brace. If he had to come off like he did, it suggests there's something there. But we'll wait for the scans on Sunday or Monday."

Sio joins the Brumbies injury list which already includes Kyle Godwin (broken hand), Jordan Smiler (hamstring) and Lausii Taliauli (knee).

Smiler was expected to miss at least two weeks but if he recovers faster than expected he could force his way back into selection contention to play against the Blues.

The Brumbies will have their hands full trying to stop a Blues side boasting cross-code superstar Sonny Bill Williams after he recovered from an Achilles injury that ruined his sevens Olympic Games campaign last year.

Australian teams have lost the first 13 trans-Tasman matches this year and the Brumbies haven't beaten a New Zealand side since round one last year.

The Brumbies have attempted to shift their mindset to attacking rugby in recent weeks but they are still finding the balance between risk taking and tactical decisions.

"We've tried to be better with ball in hand over the last couple of weeks and I think we've shown that," Larkham said.

"We probably slipped up against the [Melbourne Rebels] two weeks ago where we got a bit sloppy but I'm still very proud of the way we've attacked. We've got some work to do, but it's been pleasing the way the guys have changed that mind set.

"There's no magic formula. It's just about getting back and working hard to put ourselves in a good position."