Valetini is expected to be ruled out for a handful of weeks after damaging ligaments in his knee in the Brumbies' tight win against the NSW Waratahs in Canberra last week.

The full extent of the damage will be known when he has scans on Monday after another devastating injury blow for the 20-year-old just days after signing a two-year contract extension.

The injury has given Brumbies coach Dan McKellar another unexpected headache, with Pocock (calf) unlikely to play against the Queensland Reds on Sunday and Ben Hyne unavailable for the season after knee surgery.

Blake Enever, Murray Douglas and New Zealand recruit Jahrome Brown will give the Brumbies cover on the bench, while Pete Samu is set to earn his second start of the season.

Pocock has played three of five games so far this year, leaving the field after five minutes in round one with concussions and limping off with a calf strain against the Melbourne Rebels two weeks ago.

The good news for the Brumbies, and perhaps a strange omen, is that the only games they have won this year are the ones Pocock hasn't played.

It's unlikely the Brumbies will rush Pocock back on to the field given it's so early in the season and they have a bye after playing the Reds at Suncorp Stadium.

"One thing it gives us is confidence, understanding we're a team and we don't rely on individuals," McKellar said. "I'm sure we'll win a couple when David's back as well."

Samu is a handy replacement to have for the starting XV while Lachlan McCaffrey is emerging as a Wallabies contender and Tom Cusack continues to impress at No. 7.

Brown was added to the Brumbies extended squad after Hyne's injury in the pre-season and Douglas, a former Rebel and Hurricanes big man, is rated highly by McKellar.

Enever has also spent time at blindside flanker in the past and could be another option to add more bulk to the Brumbies forward pack.

Valetini's awkward knee injury was the only sour note to the Brumbies' impressive win against the Waratahs, which ensured the club avoided three losses in a row.

"My fingers are crossed he just got a bit of a fright but he's in a brace," McKellar said of Valetini.

"There's potential to be some damage, but I don't think it's medial ligament which has been his problem in the past. Rob is going to miss a few weeks, but we're hopeful it's not going to be long term."

Valetini played just three games last year after twice damaging his medial ligament. "I hope he's all right. He's a good player, a good kid ... hopefully he's back on the park soon," said Wallabies captain Michael Hooper.

The Reds got their first win of the season when they came from behind to beat the Japan Sunwolves 34-31 on Saturday and they'll be determined to upset the Brumbies on home turf.

McKellar will be faced with more selection conundrums for the match after rotating his squad for every game of the year so far. The Brumbies are yet to have the same starting XV for two games in a row and that will be the case again this week because of Valetini's absence.

Samu, a two-time Super Rugby champion, has been forced to bide his time on the bench in four of the five games since leaving the Canterbury Crusaders to link with the Brumbies.

"To be honest, whether I'm starting or on the bench, I just try and get out there and do the best for the team," Samu said.

"Yeah definitely looking to [start more often], you always want to try and start for the teams but being in the 23 I'll take that anyway.

"If [Valetini's injury] it does [give me a chance], I'll leave that up to the management and staff but I think I'll just try and get better every week and if it comes, it comes and I'll put my best foot forward for the team."

Scott Sio and Tom Cusack have been cleared of any major injuries and are expected to be free to play against the Reds. Toni Pulu is also edging closer to a return after fracturing his cheekbone in round one.

Allan Alaalatoa is still recovering from a wrist problem and will miss at least one more game, giving rookie Tom Ross a chance to keep his place on the bench.

SUPER RUGBY ROUND SIX

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