Pocock and Alaalatoa flew to Sydney on Saturday morning to link with the Wallabies for a World Cup-planning camp but their first meeting will be with medical staff to assess calf and wrist injuries.

Brumbies coach Dan McKellar was forced to unexpectedly substitute Pocock in the second half of their three-point loss to the Melbourne Rebels on Friday night.

Pocock first aggravated his calf during a Wallabies camp in January. It was one of several soft-tissue injuries to Wallabies players which have been a source of angst between Super Rugby clubs and Rugby Australia.

It's unlikely the Brumbies will risk further damage to Pocock if he is not 100 per cent fit for the clash against the NSW Waratahs this week given the Wallabies camp means the club has just two days of preparation with a full squad.

Alaalatoa came off at the same time as Pocock and appeared in serious pain, but Brumbies medical staff were hopeful there was limited damage to the ligaments in his wrist.

Pocock and Alaalatoa are key members of the Wallabies' World Cup plans and the Brumbies will be forced to rest them from some Super Rugby games this year.

Pocock has already been rested for one week, as well as being concussed after five minutes in round one, but Alaalatoa has played all four games so far.

The injury concerns come at a horror time for the Brumbies, who are desperate to beat the Waratahs at Canberra Stadium on Friday night after another heartbreaking loss to the Rebels. It leaves them with one win from four games this year.

"Allan just needs to get scans to see if there's any damage to ligaments, but we won't know until we've seen those," McKellar said.

"There's a bit of uncertainty there, but the medical staff were more positive on Saturday morning than they were on Friday night.

"Poey's calf tightened up, he was pretty sore. Again, we've just got to get it scanned and see what comes back or if there's any damage. I don't want to preempt anything there."

The injury woes gave McKellar another headache after his side failed to execute, squandering a big first-half lead to lose to the Rebels 29-26 in Melbourne.

It leaves the Brumbies scrambling to save their season after winning just one of three games this year, falling to the Rebels twice in close games and being thrashed by the Wellington Hurricanes.

McKellar's frustration is exacerbated by the fact the Brumbies have shown good signs in most of those matches, including dominating the first half of both games against the Rebels.

They led 19-3 after the first 40 minutes in Melbourne, but failed to cope with momentum changes and pressure as the Rebels overpowered the visitors to secure their fourth win in a row against the Brumbies.

"I'm not going to lie, it is frustrating. That's the challenge for us - coming out of half-time at 19-3 and then execute the kick-off, be the first to score points, it would have been a different game," McKellar said.

"We've got to stay tight as a group and understand that we're not pointing the finger at individuals, it's a collective responsibility.

"We won't get a lot of time to review things this week with most of the group being away, but individually the boys need to look at the key moments and what we would do differently.

"The game plan we had in the first half was working, but we went away from it. We lacked a bit of composure."

SUPER RUGBY ROUND FIVE

Friday: ACT Brumbies v NSW Waratahs at Canberra Stadium, 7.45pm. Tickets available from Ticketek.