A recurring knee injury has again sidelined Queensland fullback Peter Hynes - but Reds coach Ewen McKenzie stops short of describing it as career-threatening.

McKenzie faces arguably his most challenging week as a coach following Queensland's disastrous 30-6 last round Super Rugby thrashing by NSW Waratahs in Sydney.

As he goes back to the drawing board with his Reds gameplan, McKenzie must also contemplate the loss of Hynes, captain James Horwill (ankle), Scott Higginbotham (calf), Rod Davies (cheekbone/hip) and Eddie Quirk (ribs) ahead of Saturday night's away clash with bogey side ACT Brumbies.

Hynes is his biggest concern.

More scans this week will determine how long Hynes will be sidelined, but McKenzie admits the fullback is struggling mentally.

"I am feeling for him at the moment," McKenzie said on Monday.

"You do the work, do the rehab, get out there and have a recurrence - it's quite mentally difficult.

"It will take us a couple of days to see exactly where he is at."

Asked if it could be career-threatening, McKenzie said: "He has had a few episodes - I know if you keep having a problem it distracts you big time.

"But what we have to do is investigate it medically and at the moment it looks like a similar injury.

"We need to see if there is any other way to do it to get a permanent fix.

"But we have a very good medical crew who put a lot of time and effort into that - the frustration is felt by them too."

McKenzie hoped Horwill would be available for their March 18 clash with the Melbourne Rebels following a fourth round bye after scans showed ankle ligament damage.

Scan results this week will determine the availability of his remaining injury concerns.

The thumping loss to the Waratahs provided a wake-up call for Queensland - and it seems there will be no respite against the Brumbies.

They have never beaten the Brumbies in Canberra and only tasted victory once against ACT - way back in 1998 - in 16 matches.

That horror run does not look like changing unless McKenzie tinkers with a gameplan he admits is not "relevant" this season, despite it earning them a shock fifth placing in 2010.

"They (ACT) have been the most difficult team for us over the last 15 years or so - we have struggled against them," he said.

"Not only do we have our own challenges in terms of getting a more relevant game, we also have to take on a team that has been our biggest bogey.

"That makes for a challenging week.

"But it will define you as a group if you can overcome those circumstances - I will be laying that challenge down to the players."

McKenzie was confident the Reds could bounce back.

"Last year you could spend a lot of time thinking about attack," he said.

"Right now the game is about the breakdown, the collision moments and what happens there.

"The Rebels proved you can do a lot in a week - we are quite confident we can make the necessary adjustments."

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