The Wallabies must make at least two enforced team changes after winger Dylan Pietsch was forced out of the grand slam spring tour of Europe with a calf injury.
Pietsch is on his way back home to Australia after hurting himself in the Wallabies' 42-37 tour-opening triumph over England at Twickenham on Sunday morning.
The Western Force recruit's disappointment is joy for Queensland Reds and Australia XV vice-captain Josh Flook, who will join the squad after impressing in a 10-10 draw with Bristol on the weekend.
"Dylan Pietsch picked up a calf injury against England and will return to Australia to begin his recovery," said a Wallabies team statement on social media.
"Josh Flook will join the squad in Cardiff."
With skipper Harry Wilson also out of Monday's clash with Wales due to concussion protocols, coach Joe Schmidt will need to make changes in the back row and backline.
Pietsch's exit will likely mean a promotion for Max Jorgensen, who scored the last-gasp match-winner against England, with Samu Kerevi, Harry Potter and Flook in contention to join the bench.
Veteran Kerevi would be making his first Test appearance since last year's ill-fated World Cup, while English-born Potter would become the 18th debutant under Schmidt.
After starting on the bench at Twickenham, Langi Gleeson looms as a like-for-like No.8 replacement for Wilson.
Schmidt, though, also has the option of moving dual John Eales Medallist Rob Valetini to the back of the scrum and Jeremy Williams from the second row to No.6 and calling on 2023 World Cup captain Will Skelton or Lukhan Salakaia-Loto to start at lock.
Williams, who has played Super Rugby at blindside flanker, said he was willing to  cover any role.
âI think if the opportunity came and I was picked to play anywhere in the field, I'd always put my hand up because it's such an honour to be able to represent your country,â said the 23-year-old Western Force captain.
âWhichever way the coaching staff goes, we've got an awesome bunch of back-rowers in the group. I think anyone will be willing to put their hand up and we'll do the job for the team.â
Schmidt also needs a new captain, with Allan Alaalatoa favoured, depending on whether the prop starts or comes off the bench as he did against England.
Wales will be without winger Mason Grady, who is set for ankle surgery after suffering the injury early in their 24-19 weekend loss to Fiji - their 10th straight defeat.
The Wallabies downed the touring Welsh twice in July and must continue their winless run this year to keep alive Australian hopes of a first grand slam sweep of the British Isles since 1984.
They face Tests against Scotland and Ireland to wrap up the tour. Â
