Loosehead Sio has a medial ligament strain and five-eighth Toomua has an ankle syndesmosis injury, with both expected to miss 6-8 weeks, which would see them miss until about round 17 - two weeks before finals.

Versatile back James Dargaville (foot) has a Lisfranc injury and will be sidelined for 2-4 weeks.

Wallabies outside centre Tevita Kuridrani (shoulder) is also out, although there are rumours he could return earlier than expected from an AC joint problem.

Two knee injuries, about two years apart, will give Brumbies prop JP Smith his chance for his run-on debut against the Melbourne Rebels at Canberra Stadium on Saturday.

The Brumbies made a conscious decision to get more out of their bench during the pre-season and Wallabies backrower Scott Fardy has "so much faith" those coming in to cover the franchise's heavy injury toll can get the job done.

It opens the door for players such as Smith to play a bigger role.

Former Brumbies coach Jake White had fellow South African Smith on his radar a few years ago, but didn't have a spot for him in the squad.

A knee injury to Smith while playing club rugby in Brisbane brought to him to Canberra to do rehabilitation and a bunch of front-row injuries allowed him to spend time on the bench.

But when White suddenly walked out on the club, Smith was left in limbo because he was yet to sign a contract.

A phone call from former director of rugby Laurie Fisher reassured him and he was contracted for 2014.

Now Sio's knee injury will give him his chance to start against the Rebels as the Brumbies look to get their season back on track after last weekend's shock loss to the Auckland Blues.

"Even before pre-season ... we all came to an agreement that the last 15-20 minutes really hurt us last year so that was definitely for the bench and our whole squad to increase our intensity when we get on the field. It's been working so far," Smith said.

Smith came off the bench and played 36 minutes against the Blues and Fardy said he played a vital role in the Brumbies' second-half fight back, even though they weren't able to get the win.

Fardy said locks Rory Arnold and Blake Enever were other examples of squad members who'd come into the starting line-up and excelled so far this season.

He was confident Smith would do the same.

"I've had so much faith in what the guys off the bench have done this year. You saw in Auckland, we brought guys off the bench early and they did such a great job," Fardy said.

"[Smith is] one of those guys that came off the bench last week and was really, really impressive. I think he made 14 tackles in about half an hour, he was incredible.

"[He's] someone who just needs an opportunity and obviously with Scotty's injury he gets that ... I hope he gets a haircut before he gets out there."

While key backs Toomua and Kuridrani are out, Fardy didn't think the forwards needed to shoulder more of the load.

In typical forward pack mentality, he said they carried the load every week anyway.

"We've got to make sure we [forwards] do what we do well and the backs do the flashy stuff at the end that I don't care about," he joked.

"As long as us forwards are good I'm fine with that. We've always got to step up and be physical and lead from the front. We've got a number of Wallabies in our side and they've got to lead by example [as well]."

SUPER RUGBY ROUND 10

Saturday: ACT Brumbies v Melbourne Rebels at Canberra Stadium, 7.40pm. Tickets available from Ticketek.