The 208 centimetre twin brother of Brumbies teammate Rory is a round-one bolter for the Brumbies' clash against the Japan Sunwolves in Tokyo on Saturday.

The Brumbies will name their team on Thursday, with Richie Arnold the front-runner to partner Sam Carter in the starting XV and Rory to be the back-up muscle on the bench.

It would be a massive reward for Arnold's impressive pre-season after signing a deal with the Brumbies when the Western Force was axed from the competition.

But Arnold's extra excitement and nerves come from the fact he was sitting in a birthing class with partner Megan Campbell less than 24 hours before leaving Canberra.

Arnold and Campbell are expecting their first child on March 19, and although there was some initial hesitation about going to Japan, Arnold is on the road for what looms as a surprise Brumbies debut.

"I did think about not going. I don't want to miss the birth, and if [Campbell] had wanted me to stay, I would have," Arnold said.

"But we were both happy for me to go, so that's exciting. It's a tough one ... I am nervous the more I think about it but I've been pushing it to the back of my mind because I'm so excited about Super Rugby.

"We were at a birthing class [on Monday], that made it more real. It's all exciting and it's all positive."

Brumbies coach Dan McKellar is set to blend new and old blood in his team for the start of the season against the Sunwolves.

Tom Cusack, Lachlan McCaffrey and Rob Valetini are competing for back-row spots, with the Brumbies searching for players to fill the holes left by Scott Fardy and David Pocock.

Christian Lealiifano will likely resume the flyhalf duties, while the Arnold twins have been in a four-way battle with Carter and spring tour Wallaby Blake Enever for game time.

Richie Arnold's rise could pave the way for the Brumbies to have the tallest lock combination in Super Rugby history if he's on the field at the same time as Rory.

Richie played seven games for the Force in his debut season last year and has impressed Brumbies coaches with his physicality in pre-season games.

"I'm feeling good, it's been pretty tough so far and now it's just about playing," Richie Arnold said.

"We've been all getting stuck into each other. A few of our training sessions, I pulled up like we'd just played a full game.

"I feel like I'm ready to go and my body can handle the contact this year. I'll just throw myself out there and hope for the best. It's time to have a crack."

The Sunwolves have won just three games since joining Super Rugby three years ago, but have added South African forwards Willie Britz and Wimpie van der Walt to their squad to bolster the forward pack.

However, former Brumbies prop Ruan Smith has left the Sunwolves due to family reasons and won't play for the club this season.

The Brumbies will play their first three games on the road against the Sunwolves, Queensland Reds and Melbourne Rebels before returning to Canberra for a run of six out of seven games at home.

Arnold could be one of several recruits from the Force to be injected into the Brumbies' side this weekend, with Isi Naisarani and Chance Peni also pressing their claims for selection.

SUPER RUGBY ROUND ONE

Saturday: Japan Sunwolves v ACT Brumbies at Prince Chichibu Memorial Stadium, Tokyo, 3.15pm. TV time: Live on Fox Sports.

Brumbies team: 15. Tom Banks, 14. Henry Speight, 13. Tevita Kuridrani, 12. Kyle Godwin, 11. Chance Peni, 10. Christian Lealiifano, 9. Joe Powell, 8. Isi Naisarani, 7. Tom Cusack, 6. Rob Valetini, 5. Sam Carter, 4. Richie Arnold, 3. Allan Alaalatoa, 2. Josh Mann-Rea, 1. Ben Alexander. Reserves: 16. Robbie Abel, 17. Faalelei Sione, 18. Les Leuluaialii-Makin, 19. Rory Arnold, 20. Lachlan McCaffrey, 21. Matt Lucas, 22. Wharenui Hawera, 23. Lausii Taliauli.