Skipper Allan Alaalatoa and lock Nick Frost have returned to the fold from injury and will be utilised as impact players off the bench against the Waikato Chiefs.

Following back-to-back wins against Kiwi sides, the side are hunting their third on Saturday and coach Dan McKellar has flagged it as their "biggest challenge to date".

Alaalatoa has been itching to get back on the field, having been out since round eight with a neck injury, and he could not help himself during the Brumbies 17-point triumph last week.

"He's certainly not the greatest spectator, he likes to be out there. He's done a good job running the water," McKellar chuckled.

"But his primary role is to be dominant at set piece and produce a whole lot of physicality, and he's keen to do that."

Numerous forwards have put their hand up in his absence, leading to an undefeated run since their round-seven loss to the Queensland Reds, and it has not gone unnoticed by McKellar.

"It's a credit to the depth we've got in the squad," he said.

"[Tom Ross] and [Sefo Kautai] have done a great job but it's good for Al to freshen up and be ready to go for the back end."

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McKellar has made two changes to his starting XV for the round 12 clash, with James Slipper and Folau Fainga'a earning themselves a start in the forwards rotation.

The Brumbies will rest four players with Lachlan Lonergan, Tom Ross, Luke Reimer and Hudson Creighton staying behind in Canberra.

Scott Sio has been pushed to the bench in the forward rotation, but Billy Pollard and Rory Scott are both back in the mix for the Chiefs game.

Frost will join them, as he makes his return from a three-week absence as an impact player off the bench. His knee had been giving him grief, which the Brumbies "could've pushed through", but decided against it.

"It's best to look after him, and make sure he's not on one leg for the second half of the season," McKellar said.

"We've been reasonably lucky in and around injury. We've had our bumps and bruises and certainly had guys out but we haven't had too many, three months or longer.

"Across the board, we're in pretty good health. We said after reviewing trans Tasman last year that we need to be healthy and we're doing okay at the moment."

Australian Super Rugby sides' squad depth and physicality for the full 80 minutes continues to be tested against the Kiwi teams.

McKellar knows this is where many of the battles against their New Zealand opposition will be fought, and that was why having such talent on the bench was crucial.

"I know for a fact that the New Zealand teams like to think that they can run over the Australian teams in the last 20 minutes and that'll be the plan with the opposition again this week," he said.

"So how our finishers come on and make a positive impact, at the same time bring control and discipline ... is incredibly important.

"We know if we dominate that last 20-25 minutes, then we give ourselves a good chance of winning."

Sunday: Waikato Chiefs v ACT Brumbies at Waikato Stadium, Saturday 5.05pm AEST

Brumbies team: 1. James Slipper, 2. Folau Fainga'a, 3. Sefo Kautai, 4. Darcy Swain, 5. Cadeyrn Neville, 6. Rob Valetini, 7. Jahrome Brown, 8. Pete Samu, 9. Nic White (c), 10. Noah Lolesio, 11. Andy Muirhead, 12. Irae Simone, 13. Len Ikitau, 14. Tom Wright. 15. Tom Banks.

Reserves: 16. Billy Pollard, 17. Scott Sio, 18. Allan Alaalatoa, 19. Nick Frost, 20. Tom Hooper, 21. Rory Scott, 22. Ryan Lonergan, 23. Ollie Sapsford.