Carter has been picked in a World XV team to play against Japan in Osaka on Friday night in a match which will also double as a farewell for retiring Brumbies teammate Ben Alexander.

Ideally, Carter would be in Tokyo with the Wallabies for a Bledisloe Cup contest and setting his sights on the World Cup next year.

But the workhorse second-rower has fallen off Test coach Michael Cheika's radar and hasn't played for the Wallabies in almost 18 months.

The Brumbies have given Carter an extended break from games, opting to rest him through the National Rugby Championship to allow him to overcome niggling back and shoulder problems.

But time away from the game has sparked Carter's enthusiasm to get back on the field, with his World Cup ambitions appearing to hinge on dominating Super Rugby next year.

"It has been tough and it's been happening every year, but I just took a focus on doing everything I could to get my body right and helping out around the club," Carter said.

"I just wanted to get right again. I got this opportunity to play against Japan with a lot of talented people, it's good to get a taste of playing at this level and I'm really excited about it.

"Keeping fit was part of the deal, trying to put on some weight as well. Just a couple of extra kilos to get some my strength back to rip in and get ready for next year."

Carter's Wallabies future will likely have a major bearing on his next career move, with the 29-year-old off-contract at the end of the 2019 Super Rugby season.

Cheika has chopped and changed with lock combinations over the past two years, but seems settled on the quartet of Adam Coleman, Izack Rodda, Rob Simmons and Rory Arnold.

Carter can force his way back into contention with a strong Super Rugby season, but he is yet to speak with the Brumbies or Rugby Australia about his long-term playing options.

The Brumbies have all but finalised a deal to keep prop Allan Alaalatoa in Canberra until the end of 2023 in a boost for the club's long-term plans.

But there are a host of players, including Carter, Christian Lealiifano, Henry Speight, Scott Sio and Tevita Kuridrani, who will also be searching for new deals at the end of a World Cup cycle.

Former Wallabies coach Robbie Deans will take the reins for the World XV, which also boast Brumbies recruit Toni Pulu.

Japan will be using the game as a warm up before their match against the All Blacks next week, while Alexander will get the chance to play again after announcing his retirement two months ago.

Alexander, the most capped player in Brumbies history, was a late addition to the World XV squad and he'll link with Deans a decade after he picked Alexander for his Test debut.

The timing of Alexander's retirement meant he didn't get a chance to farewell Brumbies or Australian rugby fans, but Carter says the 154-game prop is still in brilliant condition.

"To get one last game with him here in Japan is great. He's looking trim ... career-best nick I reckon," Carter laughed.

"[Alexander's retirement] happened pretty suddenly, but it's great to have big 'Des' back in the fold. He's back for one more time, a bit like John Farnham, so it's exciting to play with him again."

Carter was also excited to link with former Waikato Chiefs speedster Pulu, who will move to Canberra next month to start pre-season training with the Brumbies.

"I met him earlier in the week and I've loved what I've seen of him so far," Carter said. "He's been really good to train with and I'm really looking forward to playing with him in Japan."

The World XV side will also boast Andy Ellis, Nehe Milner-Skudder, Adriaan Strauss and Leonardo Senatore.