The Brumbies were forced to finish their game against the Otago Highlanders with 14 players after match officials refused to allow them to replace Isi Naisarani, who had failed a head injury assessment test.

Tom Cusack came back on to the field when Naisarani was being tested, but was told he must return to the bench when Naisarani was diagnosed with concussion.

The decision had no impact on the final result given it was in the last five minutes and the Highlanders were well ahead.

But it highlighted a lapse in the concussion crackdown as all sporting codes implement strategies to offer better protection to players.

The Brumbies asked for clarification on the ruling and were told Cusack should have been allowed to stay on the field.

Naisarani has been cleared to play against the Argentina Jaguares at Canberra Stadium on Sunday after passing the return to play protocols last week.

Brumbies captain Sam Carter will also be returning to the starting side for the first time in six weeks after being concussed against the Melbourne Rebels in March.

"The [incident] last week was kind of confusing ... I think they've cleared it up this week though," Carter said.

"I think player safety is paramount these days and if a bloke is [concussed] and can't return, I think there are rules and guidelines around that to make sure you can cover those situations."

Carter will shoulder the captaincy duties when he returns to the starting side after the Brumbies opted to co-skipper Christian Lealiifano.

He is one of four changes to the starting XV, with Joe Powell returning to scrumhalf, Henry Speight on the wing to play his 100th game and Kyle Godwin replacing Lealiifano.

The Brumbies surprised Speight at training on Saturday, with dad Sam flying to Canberra to present the winger with his jersey before he becomes the first Fijian to reach the 100-game milestone.

Coach Dan McKellar has also added fresh blood to the bench, with rookies Mees Erasmus and Darcy Swain set to make their Super Rugby debut if they get on the field.

Swain is a Brisbane junior who moved to Canberra for a chance to train with the Brumbies and is a former Australian under-20s lock.

The 20-year-old faces a daunting initiation against an Jaguares forward pack known for its uncompromising style and hard-nosed approach to the game.

"I was here for Darcy's first NRC game and he's had a really strong pre-season here. I'm looking forward to seeing how he goes," Carter said.

"He's a bit loose, he throws himself into pretty much every contest. He's not afraid of stepping up and doing the dirty work or the tough stuff."

McKellar is confident the changes made can help spark the Brumbies again after they hit a hurdle against the Highlanders.

"Joey [Powell] and Matty [Lucas] ... there's not a great deal between them," McKellar said.

"Matt has had a couple of starts and Joey has been finishing the games. We'll change their roles around this week and that's a decision with how we intend to play, we feel Joe will be best for us in the first 60 minutes [against the Jaguares]."

SUPER RUGBY ROUND 10

Sunday: ACT Brumbies v Argentina Jaguares at Canberra Stadium, 4.05pm. Tickets from Ticketek.

Brumbies: 15. Tom Banks, 14. Henry Speight, 13. Tevita Kuridrani, 12. Kyle Godwin, 11. Chance Peni, 10. Wharenui Hawera, 9. Joe Powell, 8. Isi Naisarani, 7. David Pocock, 6. Tom Cusack, 5. Sam Carter, 4. Rory Arnold, 3. Allan Alaalatoa, 2. Folau Faingaa, 1. Scott Sio. Reserves: 16. Robbie Abel, 17. Mees Erasmus, 18. Nic Mayhew, 19. Darcy Swain, 20. Michael Oakman-Hunt, 21. Matt Lucas, 22. Jordan Jackson-Hope, 23. Andrew Smith.

Jaguares: 15. Joaquin Tuculet, 14. Ramiro Moyano, 13. Matias Orlando, 12. Jeronimo De La Fuente, 11. Emiliano Boffelli, 10. Nicolas Sanchez, 9. Gonzalo Bertranou, 8. Javier Ortega Desio, 7. Marcos Kremer, 6. Pablo Matera, 5. Tomas Lavanini, 4. Guido Petti, 3. Nahuel Tetaz Chaparro, 2. Agustin Creevy, 1. Santiago Garcia Botta. Reserves: 16. Julian Montoya, 17. Javier Diaz, 18. Juan Pablo Zeiss, 19. Matias Alemanno, 20. Leonardo Senatore, 21. Martin Landajo, 22. Bautista Ezcurra, 23. Bautista Delguy.