Wales assistant coach Jonathan Thomas warned on Wednesday that Australia would be like a "wounded animal" before this weekend's high-stakes Rugby World Cup game in Lyon.

The Wallabies need to win on Sunday if they are to keep their hopes of reaching the quarterfinals alive after last week's 22-15 upset loss to Fiji.

Wales top Pool C after beating the Pacific Islanders as well as Portugal.

"Confidence, for me, comes from the work you do during the week," former Wales back-rower Thomas told reporters.

"That is where we get our focus from.

"We respect Australia as a rugby nation, they are a wounded animal, they can be dangerous," he added.

Wales can almost guarantee a last-eight spot by beating Eddie Jones' side this weekend before they end their pool campaign against Georgia, ranked 13th in the world, on October 7.

"It is a cliche, and I apologise, but you just have to focus on yourselves," Thomas said.

"When you start thinking about permutations or selections of the opposition, you go down a rabbit hole, in my opinion," the 40-year-old added.

BACK-ROW OPTIONS

Wales, who finished fourth in the 2019 World Cup, have just one injury concern before the game, with flanker Tommy Reffell suffering from a calf issue.

If Reffell is passed fit, head coach Warren Gatland could decide to start him alongside Jac Morgan in the back row, allowing Wales to have two specialist opensides on the field.

The move would benefit Gatland's team in their attempt to slow down Australia's possession at the breakdown.

"You are asking for the team, aren't you? I am not going to give it to you," Thomas jokingly said, with Wales not due to announce their line-up until Friday.

"The good thing we've got with our back-rowers is that they are versatile, all of them can play in different positions, pretty much, so those options are always there. We'll see," he added.

Experienced centre George North is expected to feature against the Wallabies.

North is looking for just his fifth win in 16 games against Australia, for his country as well as for the British and Irish Lions.

The 31-year-old faces competition from Nick Tompkins, Mason Grady and Johnny Williams for a spot in Gatland's midfield.

"The quality we have got now is really showing," North said.

"Each day everyone is trying to get better to fight for that jersey, and that's what drives you on."