Coach Dan McKellar is hopeful Lachlan McCaffrey and Lolo Fakaosilea will be cleared to play against the Melbourne Rebels after both copping knocks in a frustrating loss to the Queensland Reds.

Flanker Tom Cusack also had to leave the field after a head knock and McKellar will be forced to call on reinforcements form outside of his squad if just one of the trio is unable to play against the Rebels.

David Pocock and Rob Valetini are both recovery from knee injuries, leaving Cusack, McCaffrey, Fakaosilea and Isi Naisarani as the only fit back-rowers with contracts.

McKellar hoped to find out on Sunday if McCaffrey or Fakaosilea had suffered serious damage before what looms as a crucial clash in Melbourne on Friday night.

"We'll see how they pull up, we don't want to be losing too many more back-rowers that's for sure," McKellar said.

"We're not sure where they are yet, hopefully we don't have to get anyone in. Hopefully [the injuries] settle down over the next couple of days, Locky played 60 minutes with it so you'd like to think that's a good sign."

Christian Lealiifano played just 45 minutes in Queensland, but McKellar said that was part of a plan to manage his work load rather than injury concerns.

The Brumbies had their pride dented against the Reds, losing 18-10 despite scoring the only two tries of an absorbing Australian conference contest.

It sets the stage for an important match against the Rebels, who continued their impressive start to the season with a bonus-point win against the Japan Sunwolves on Saturday.

A win against the Rebels is critically important to gain confidence and momentum before the Brumbies play their first home game of the year, and also to ensure prevent a gap opening up in the Australian race.

The Brumbies were well below their best in Brisbane, overpowered at scrum time and then failing jto hold the ball long enough to be a real threat to the Reds' defence.

"We're not going to jump at shadows. But if we're honest with each other [the game against the Reds] wasn't at our standard," McKellar said.

"I thought our defensive effort was outstanding, but in attack we just needed more spark. When you work so hard to get the ball, you've got to have the spark and energy to take the opportunity.

"You've got to keep believe in what you're doing, train well, demand higher standards and have a thorough review. You've got to understand we're doing some things well, but need to do others better."

Brumbies captain Sam Carter added: "[The Reds] kicked six penalty goals, that's always going to hurt and if we don't execute under pressure that's what will happen."

The Rebels seem to thrive on matches against the Brumbies, shocking the visitors in Melbourne last year when everyone tipped an easy ACT win.

But the Brumbies could be bolstered by the return of Wallabies prop Scott Sio this week after his start to the season was delayed by a calf injury.

Sio's presence would help stabilise the wobbling scrum, which struggled to match the Queensland pack in the second half in what was ultimately a turning point in the clash.

"There were too many set-piece turnovers, simple errors and dropped ball," McKellar said.

"It was frustrating. We pride ourselves on being able to problem solve on the run [in the scrum] and we failed to do that."

SUPER RUGBY ROUND FOUR

Friday: Melbourne Rebels v ACT Brumbies at AAMI Park, Melbourne, 7.45pm. TV time: Live on Fox Sports.