Back-to-back losses for the first time in two years have prompted the biggest Brumbies' reshuffle of the season, adding Clyde Rathbone, Pat McCabe, Ruan Smith and Fotu Auelua to the starting XV.

Fullback Jesse Mogg and Leon Power have been dropped to the bench, prop Ben Alexander is managing a neck injury, and Robbie Coleman is recovering from gastro.

The Brumbies need to win their last three games of the regular season to make the finals, starting with a clash against the Melbourne Rebels on Saturday night.

"We were in a reasonably dark place when we got back [from a two-game tour of South Africa], but the clouds have lifted," Fisher said.

"It's important to have the maximum number of players who are playing well ... the Rebels challenge you physically, so we need a certain amount of freshness and need to power up a bit in our game.

"When you lose two games in a row and you've been on a two-week tour, you have to make changes. If we had won both games we probably would have made changes anyway."

Wallabies back McCabe gets his first chance in the starting side for the first time in a month after he was forced to bide his time on the bench to make way for Christian Lealiifano.

McCabe had an outstanding start to the season as the Brumbies' inside centre while Lealiifano was recovering from ankle surgery.

His form was so good he was added to the Wallabies squad for the June Test series against France, despite having to make an impact from the bench.

McCabe, who has broken his neck twice in the past two years, will move to fullback to replace Mogg, who's down on confidence after an inconsistent season.

Fisher backed Mogg to recapture his best form in the coming weeks, while Rathbone rated McCabe as the toughest player he'd seen.

The Rathbone-McCabe duo will likely mean less kicking from the Brumbies, with both players known more for their hard-running style than their kicking ability.

"I don't think Patty and I are getting picked for our kicking game," Rathbone said.

"We're just going to have to carry strong and try to get gain line; that's something that has underpinned our success in the past few years.

"Patty is one of the toughest guys I've played with and one of the hardest workers away from the game. He gives us direct, hard-running that's crucial. It's an indication of how much depth we've got in our backline."

Smith will take over the tighthead prop duties while Alexander battles through a neck injury, which could hinder his Test campaign next month.

The Brumbies have struggled in the past two weeks, leaking 71 points against the Free State Cheetahs and the Pretoria Bulls.

They've won just one of their past four games and have slipped outside the competition's top six for just the third time in three seasons.

Fisher said the team was refusing to panic, but admitted there was pressure to perform in the clash against the Rebels.

"The 'what' [is going wrong] is easy, but the 'why' isn't," Fisher said.

"Some things just happen and if you look too hard for answers ... it's like hunting a Snark, you'll never find them. They don't exist.

"We've tinkered ... it's not overhauling. Everyone was a bit tense early in the week; it's easy enough to only focus on this game but that in itself brings pressure. There's absolute pressure in needing to get a result this weekend."

SUPER RUGBY ROUND 16

Saturday: ACT BRUMBIES v MELBOURNE REBELS at Canberra Stadium, 7.40pm.

BRUMBIES TEAM: 1. Scott Sio, 2. Stephen Moore, 3. Ruan Smith, 4. Sam Carter, 5. Scott Fardy, 6. Fotu Auelua, 7. Jarrad Butler, 8. Ben Mowen, 9. Nic White, 10. Matt Toomua, 11. Clyde Rathbone, 12. Christian Lealiifano, 13. Tevita Kuridrani, 14. Henry Speight, 15. Pat McCabe. Reserves: 16. Josh Mann-Rea, 17. Jean-Pierre Smith, 18. Ben Alexander, 19. Leon Power, 20. Jordan Smiler, 21. Michael Dowsett, 22. Andrew Smith, 23. Jesse Mogg.