Frost is set to make is Brumbies starting debut in what will be just the third game of his career. He'll be joined by Bayley Kuenzle, who steps into the No. 10 jersey for the first time to replace Noah Lolesio.

The first-year duo get their opportunity against the Western Force and McKellar has faith in the new breed, although it must have been tempting to go back to the future on Wednesday.

Nic White and Christian Lealiifano lingered as the last two players on the field after training on Wednesday, doing the little extra that have become routine over almost a decade.

McKellar resisted the urge to tap the World Cup teammates on the shoulder and say: "come on fellas, let's get the band back together."

But White has just finished a 14-day quarantine and Lealiifano is training for fitness, so it's their presence that will be important when the Brumbies make changes for the Force.

Kuenzle, a former junior Wallaby, can tap into both White and Lealiifano for guidance ahead of his starting XV debut while Frost, a 205 centimetre 20-year-old, is itching to help rectify lineout woes.

The Brumbies lost 8 of their own lineout throws last weekend, setting the stage for Frost to show his lock worth when the former Canterbury Crusaders prospect steps up to the next level.

The opportunity was almost lost. Frost broke his foot just as the Brumbies started to ramp up training after the coronavirus shutdown.

"After the X-ray I had a look at it myself and I saw it was only a little break, so I hoped I didn't need surgery and I didn't. In the end I haven't missed much, so it's not the end of the world," Frost grinned.

The Crusaders saw something special in Frost three years ago when they swooped to snatch him away. After 18 months in Christchurch, the Brumbies lured Frost back and he made his debut in round two.

Now, after just 16 minutes of Super Rugby and without having played a game since March, Frost is expected to get his opportunity alongside Murray Douglas as the Brumbies aim to remain unbeaten.

"I'm keen just to get out and play regardless of where it is," Frost said. "It's a bit of a shock, it's going to be a bit weird being involved in everything but I'm keen.

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"We played the Force in the [National Rugby Championship final] so they're going to rip in. It gives you a bit of confidence knowing I've played them before, and personally I think I'm ready to have a crack."

McKellar will name his team on Thursday, with the Brumbies keeping White on ice for at least this week given they also boast Joe Powell, Issak Fines and Ryan Lonergan as scrumhalf options.

James Slipper is expected to be cleared to play after suffering a concussion last week, but he could rotate out of the starting front-row as part of his combination with Scott Sio.

The Brumbies and Force will meet for the first time since 2017 when they play at Leichhardt Oval. The teams built a strong rivalry when the Perth side joined Super Rugby and poached Matt Giteau as their marquee man.

Now they're back in the Australia-only competition and the memories of their World Club 10s battle, NRC contests and a bitter end to the Force's time in Super Rugby will drive both teams ahead of the match.

SUPER RUGBY AU ROUND FOUR

Saturday: Western Force v ACT Brumbies at Leichhardt Oval, 7.15pm