Accomplished assistant coach Tabai Matson revealed the Flying Fijians have been preparing as if the Wallabies will field openside flankers Michael Hooper and David Pocock in their starting pack for Saturday's clash in Sapporo.

Matson said his team's hard work through an extended southern hemisphere winter together had them quietly confident they can live up to the dark horse tag bestowed on them.

"Could we achieve an upset? If we prepare well and click on the day, it'll be a good game and we have a chance," he said.

"We feel a bit like David and Goliath, but we'll see.

"You look at Pocock and Hooper and a number of other Wallabies, and they are world class so the breakdown is something we've focused on for the last two months."

Fiji are no mugs themselves in the back row, with captain Dominiko Waqaniburotu among his country's most consistently impressive players in accruing 45 caps.

He should be joined by another star of the French club scene, Viliame Mata, and Harlequins flanker Semi Kunatani. Mata and Kunatani were in the Fijian sevens team who won a historic gold at the Rio Olympics.

All three are athletic but have added a ball-winning element to their game under the eye of head coach John McKee and fellow-Kiwi Matson, who has previously coached at Canterbury and the Crusaders.

Matson is convinced Fiji will be a more formidable than the side who suffered double-figure losses to Australia, England and Wales at the previous World Cup.

With four more years of top flight European rugby under the belt of many players and the addition of stars such as prolific former NRL tryscorer Semi Radradra, Matson believes a considerable improvement looms from his ninth-ranked side.

"You have to deliver when it matters and we missed moments against England and against Wales - and you just can't do that," Matson said.

"(Since then) World Rugby have done a fantastic job with the support to tier two teams and that has had an effect. We are definitely better prepared and the margins have closed."

Australian Associated Press