It's understood the ACT Brumbies expect the back-rower to miss between six and eight weeks after having scans on his third knee injury of the past 13 months.

The good news is it's a different injury to the medial ligament he damaged twice last year, but it's still a cruel blow for the 20-year-old who signed a two-year contract extension last week and was invited to a Wallabies training camp in Sydney.

Wallabies coach Michael Cheika has been keeping a close eye on his development, although the Brumbies have warned against expecting too much too early from the powerfully-built flanker.

The Brumbies have 11 games left in the Super Rugby season, including a clash against the Queensland Reds in Brisbane on Sunday afternoon.

Valetini's injury will limit his time to impress at the back end of the season and will test the Brumbies' back-row depth given Ben Hyne is already out for the entire season.

Blake Enever, Murray Douglas and New Zealand recruit Jahrome Brown are expected to bolster the back row stocks in the coming weeks as David Pocock continues to battle a niggling calf strain.

Brumbies coach Dan McKellar is considering his selection options for the chance to win back to back games for the first time this year.

Pete Samu will likely get his second opportunity to start in Valetini's absence, joining Lachlan McCaffrey and Tom Cusack as the back-row trio.

But there are other positional headaches across the field, particularly with wingers lining up to get their chance to make their mark on Super Rugby this year.

Toni Pulu is working in the background to make his comeback from a fractured cheek, which could come as early as the clash against the Canterbury Crusaders on April 4.

Pulu was the unlucky Brumbies recruit who clashed heads with Billy Meakes in the first 10 minutes of the season, resulting in a trip to hospital and surgery to repair the damage.

But fellow winger Henry Speight said the Wallaby-in-waiting said Pulu was still setting speed records at Brumbies training.

"I think he set a team best on the weekend for the 10 metre dash, so he's itching to get back," Speight said of Pulu.

"The boys who aren't playing are very good at helping out with review and preview stuff, identifying what we might be up against [each week]. It's a tough environment but it's also good to have guys who will help out in that way."

The Brumbies have stuck with the same wing combination just once this season, with Chance Peni and Andy Muirhead playing against the Melbourne Rebels and Waikato Chiefs.

Speight (hip) and Pulu (cheek) were injured in round one, while Lausii Taliauli (knee) made his comeback last weekend and young gun Mack Hansen made his debut on the bench in the same game.

"There are guys who are really pushing for selection ... that's the beauty of team sport and in our position especially, there's a lot of very good competition for selection," Speight said.

"Everyone is on each other's heels, which is only going to benefit the team as well."

SUPER RUGBY ROUND SIX

Sunday: Queensland Reds v ACT Brumbies at Suncorp Stadium, 4.05pm. TV time: Live on Fox Sports.