The Wallabies-Wales clash at England's home of rugby presents a conundrum for fans as they face the choice between the team who knocked them out of the World Cup or their enemy neighbours.

Supporting Wales is unheard of in England and the Wallabies stand to benefit if the locals decide to jump on the Australian bandwagon.

Coach Michael Cheika has warned his players to prepare for a sea of Welsh red when the teams clash in the last pool match on Saturday night (Sunday morning AEDT).

The winner will finish at the top of the pool of death and lock in a quarter-final clash with either Scotland or Japan on a more favourable side of the path to the final.

Wales coach Warren Gatland said the shackles were off now that his team had qualified for the next stage of the tournament.

But Wallabies captain Stephen Moore says Australia won't temper its intense approach as it aims to remain unbeaten.

"You never know, do you? It's a strange dynamic," Moore said when asked if English fans would support Australia.

"Our motivation has never been to see anyone to knock anyone out of the World Cup. Our motivations are for our own reasons and for making our own people happy.

"There were a hell of a lot of people in the stands in Wallabies jerseys with smiles on their faces … we're thrilled with the support we've got over here and we can feel that."

Wales assistant coach Robin McBryde wants to turn England fan Prince Harry to the dark side and get him to wear Welsh colours at Twickenham.

"It would be nice to think [England supporters will switch to Wales]," McBryde said.

"Seeing as the World Cup is this side of the world, it would be nice if we can get behind one of the home nations.

"Both my sisters have English partners and I have a brother-in-law from England, so it's not too much to ask, I don't think."

Cheika will assess battered and bruised bodies and Michael Hooper's potential suspension before deciding on a line up to play against Wales.

Winger Rob Horne remains with the squad and is being given every chance to prove his fitness after a suspected partial dislocation of his left shoulder.

It would be easy to wrap players in cotton wool with a play-off spot secured.

But beating Wales will be just as crucial given the differing paths to the final that will arise depending on results.

A loss would see Australia face two-time champions South Africa in the quarter-final.

The alternative is playing against either Scotland or Japan before advancing to a semi-final contest against the Springboks.

"The most important thing this week [is not getting caught up] and the environment we're operating in is sudden death," Moore said.

"You can't afford to look back for a moment. We're firmly focused on the Welsh Test and anything less than the preparation we had last week isn't going to be good enough.

"That's my role and the senior players' role – drive that through the week and do those little things that contribute to performance.

"It was sudden death last week and it still is. Cheik doesn't talk about winning or losing, it's more about the performance."

The Wallabies have won their past 10 Tests against Wales and are unbeaten in matches between the countries since 2008.

The Wallabies – and presumably Wales – are pushing history aside to try to get the upper hand in the World Cup battle.

And Australia are building their title run on defence, conceding just two tries in their first two matches.

Wales ran in eight tries in their first match against Uruguay, but have relied on Dan Biggar's boot for the majority of their points in wins against Fiji and England.

In fact, more than 70 per cent of points in their past two matches have been thanks to Biggar's deadly accurate goal-kicking.

Moore said faith in the Wallabies' defensive structures was helping limit the amount of penalties conceded.

The Wallabies gave away just six penalties against England, and only two of those were in kicking range.

It was a massive improvement from the 11 infringements against Fiji and the 15 times they were penalised against Uruguay.

"We have had a focus on discipline, we know that's one way of letting the opposition into the game," Moore said.

"Particularly in your own half. It's up the individuals to make good decisions. We don't want to have rules around contesting rucks, but we just want guys making smart decisions. That leads to a low penalty count."