But the Brumbies are expected to be dealt a massive blow before kick-off against the NSW Waratahs, with Wallabies prop Scott Sio likely to be ruled out of the must-win derby.

Sio has struggled to overcome a shoulder injury and did not complete the final training session in Canberra on Friday, opening the door for Nic Mayhew to get just his second start of the season.

The Brumbies had hoped Sio would recover in time to bolster their front-row, but coach Dan McKellar has thrown his support behind Mayhew to stand tall in Australian rugby's biggest game of the year.

It's understood Sio didn't travel with the team to Sydney, with Mayhew to step up for the second week in a row and veteran Ben Alexander being added to the bench.

Carter is also back in the team for the first time since the end of June after overcoming a back complaint that has limited him to just 40 minutes of rugby in the past six weeks.

The Brumbies need to beat the Waratahs and secure a winning bonus point for scoring at least three tries more than NSW. They also need the Melbourne Rebels to lose by more than eight and the Durban Sharks to stumble.

But Carter says the Brumbies must focus on one mission to avoid being distracted by finals hype.

"When you start thinking about [how many tries you have to score], you forget what you're supposed to be doing in the first place," Carter said.

"That's why we're not too worried about that sort of stuff. We just want to keep building on what we're doing and focus on the way we want to play. If we do that, we'll get a good result.

"We don't like losing at the best of times, but certainly not against the Tahs in Sydney. They got one over us in Canberra and that's not what we wanted, so we're looking forward to the contest."

Carter will start the game on the bench, with identical twins Rory and Richie Arnold to be unleashed in the last round of the regular season. Blake Enever will shift to six, while Lachlan McCaffrey will be the back-up back-rower on the bench.

The Brumbies have won three of their past four games and that confidence has translated into scoring tries, with the side crossing the line 50 times in a season for just the second time in the past 10 years.

"The boys are starting to get confident to play and when they get a chance [to score], it's pleasing for the team," said Christian Lealiifano.

"It's a massive test for us. The Wallabies are star-studded in the Waratahs back line and they'll be hard to contain, but we're confident in doing the job."

SUPER RUGBY ROUND 19

Saturday: NSW Waratahs v ACT Brumbies at Allianz Stadium, 7.45pm. TV time: Live on Fox Sports.

Brumbies: 15. Tom Banks, 14. Henry Speight, 13. Tevita Kuridrani, 12. Kyle Godwin, 11. Andy Muirhead, 10. Christian Lealiifano, 9. Joe Powell, 8. Isi Naisarani, 7. David Pocock, 6. Blake Enever, 5. Richie Arnold, 4. Rory Arnold, 3. Allan Alaalatoa, 2. Folau Faingaa, 1. Nic Mayhew. Reserves: 16. Connal McInerney, 17. Ben Alexander, 18. Les Leulua’iali’i-Makin, 19. Sam Carter, 20. Lachlan McCaffrey, 21. Matt Lucas, 22. Wharenui Hawera, 23. Lausii Taliauli.

Waratahs: 15. Israel Folau, 14. Cam Clark, 13. Curtis Rona, 12. Kurtley Beale, 11. Taqele Naiyaravoro, 10. Bernard Foley (c), 9. Nick Phipps, 8. Michael Wells, 7. Will Miller, 6. Ned Hanigan, 5. Rob Simmons, 4. Jed Holloway, 3. Sekope Kepu, 2. Damien Fitzpatrick, 1. Tom Robertson. Reserves: 16. Tolu Latu, 17. Harry Johnson-Holmes, 18. Paddy Ryan, 19. Tom Staniforth, 20. Brad Wilkin, 21. Jake Gordon, 22. Bryce Hegarty, 23. Alex Newsome.