Brumbies coach Dan McKellar said Pocock will play against the Argentina Jaguares next week, but the game against the Cape Town Stormers in South Africa on Saturday came too soon.

Instead former Waikato backrower Jahrome Brown will wear Pocock's No.7 jersey in his run-on Brumbies debut.

Brown forms part of a reshuffled backrow, with Tom Cusack switching to blindside flanker and Pete Samu to No.8.

McCaffery (knee) has dropped out of the 23 due to a medial ligament injury he aggravated in the 31-20 win over the Johannesburg Lions last weekend.

It's a blow to as the Brumbies look to get their season back on track during the South Africa and Argentina leg of their Super Rugby season.

"[Pocock] should be available next week. He's not at 100 per cent, but the Jaguares in Buenos Aires will be what we're aiming for," McKellar said.

"It was always unlikely. [For] a calf injury two weeks is generally the minimum."

But Pocock and McCaffery's absence opens the door for Brown to make his first start for the Brumbies.

The 22-year-old backrower has been on the Brumbies bench for their past three games, but will get his chance to start at Newlands.

"Brown comes in, who has performed well off the bench, gets his first start. Mr Cusack at six and Pete Samu at eight, so still a quality back row," McKellar said.

"[Brown's] physical, high workrate, he's just someone who's in the game.

"Whether it be attack or defence, he's always a typical openside flanker where he's always in and around the ball and off the back of that he has a lot of quality involvements.

"He's forced turnovers in defence, he's scored tries and had some nice touches in attack for us. It's a great opportunity for him against a quality Stormers pack."

The Brumbies are third in the Australian conference, just one point behind second-placed NSW Waratahs - although they've played one game more than their rivals.

If they can beat the Stormers they will jump above the South African team on the overall ladder and bolster their finals hopes.

McKellar said it was a "massive game" as they look to build momentum on the back of the Lions win.

Tours of South Africa, which can now include a trip to Argentina, have traditionally been tough for Australian teams.

But the Brumbies have won at least one of the two games in the past four seasons.

Last year they led the Lions before they got a series of yellow and red cards. They also beat the Pretoria Bulls.

They won both games in 2017 - the last time they visited Argentina as part of the trip.

"It's a massive game, which they all are, but this one in particular," McKellar said.

"We had a good win at home last week. It's always good to start the tour well with a good performance.

"We beat the Bulls last year and we were leading the Lions before we had a red card ... we've had success here.

"It's not a venue or a trip that scares us by any means, but we've certainly got an enormous amount of respect for the opposition and understand that we're going to have to be on our game on Saturday."

Scottish-born forward Murray Douglas comes onto the bench to cover McCaffery's loss, while Wharenui Hawera has been brought in to replace Irae Simone.

"Hawera's played and performed well in South Africa in the past and just a particular strategy that we're looking at," McKellar said.

"Having a genuine 10 coverage on the bench I thought was important."

SUPER RUGBY ROUND 10

Saturday: ACT Brumbies v Cape Town Stormers at Newlands, 11.05pm.

Brumbies squad: 1. Scott Sio, 2. Folau Fainga'a, 3. Allan Alaalatoa, 4. Rory Arnold, 5. Sam Carter, 6. Tom Cusack, 7. Jahrome Brown, 8. Pete Samu, 9. Joe Powell, 10. Christian Lealiifano, 11. Toni Pulu, 12. Tom Wright, 13. Tevita Kuridrani, 14. Henry Speight, 15. Tom Banks. Bench: 16. Josh Mann-Rea, 17. James Slipper, 18. Leslie Leuluaialii-Makin, 19. Darcy Swain, 20. Murray Douglas, 21. Matt Lucas, 22. Wharenui Hawera, 23. Andy Muirhead.

Stormers squad: 1. Steven Kitshoff, 2. Bongi Mbonambi, 3. Wilco Louw, 4. Salmaan Moerat, 5. Cobus Wiese, 6. Ernst can Rhym, 7. Pieter Steph du Toit, 8. Kobus van Dyk, 9. Herschel Jantjies, 10. Joshua Stander, 11. Dillyn Leyds, 12. Dan Kriel, 13. Ruhan Nel, 14. Sergeal Petersen, 15. Damian Willemse. Bench: 16. Scarra Ntubeni, 17. Corne Fourie, 18. Neethling Fouche, 19. Johan du Toit, 20. Siya Kolisi, 21. Justin Phillips, 22. JJ Engelbrecht, 23. Seabelo Senatla.