Both Rennie and his Wales counterpart, fellow New Zealander Wayne Pivac, have had to chop and change their sides for the Principality Stadium clash on Saturday (Sunday morning AEDT) after the spring tour battles have left their squads with a heavy casualty list.

Rennie, out to avoid the ignominy of a first winless spring tour of Europe for 45 years, has made four changes to a team who lost their inspirational leader Michael Hooper to a foot injury in the loss to England.

Pivac's side, having also lost their own warrior leader Alun Wyn Jones among 15 players made unavailable through injury, have been beaten by South Africa and New Zealand and struggled to down Fiji.

When it was put to Rennie in Cardiff on Thursday that both sides, particularly the Welsh, would be desperate to win, he responded drily: "Yes, particularly the Australians.

"I understand that (desperation) after a couple of losses and finding their way past Fiji at the weekend - but we're pretty desperate as well.

"We haven't performed as well as we've needed to against Scotland and England, and we're keen to make up for it."

Rennie has brought in replacement flanker Pete Samu to replace Hooper, trusting that he can bring his own "athletic edge" against Wales and suggesting he's "more than equipped to do the job".

And the team has been boosted with tighthead props Taniela Tupou and Allan Alaalatoa both overcoming head-knocks to line up, while hooker Tolu Latu has been promoted from the bench.

James Slipper, back at loosehead, will captain the side for just the second time, armed with high praise from Rennie.

"Everyone had told me what a high character man he is, and he's salt of the earth, really impressive. Huge amount of respect in this group and people love him," said Rennie.

"He genuinely cares about people and cares about this jersey, so it was a pretty easy choice to make him skipper."

Reds winger Filipo Daugunu will start his first Test since breaking his arm against France back in July while Waratahs' versatile centre Lalakai Foketi is set for his first cap after being rewarded with a bench place for his excellence in training.

Four European-based players are in the 23, with Rennie noting that the future of the 'Giteau law' around overseas players' representation for the Wallabies would be reviewed after the tour.

"There are negotiations that need to happen. Obviously, there's a fair bit of money these players are on over here (in Europe) but there's certainly two or three guys who have generally talked to me about the opportunity to come back home (to Super Rugby)," said Rennie.

Of his Kiwi coaching battle with Pivac - they've crossed swords in both Britain and New Zealand but not at international level - Rennie added: "I know him (Pivac), he's a good man.

"They (Wales) have got genuine on-ball presence, a pretty strong backline and an excellent back three. It is a good side."

Wallabies: Kurtley Beale, Andrew Kellaway, Len Ikitau, Hunter Paisami, Filipo Daugunu, James O'Connor, Nic White, Rob Valetini, Pete Samu, Rob Leota, Izack Rodda, Rory Arnold, Taniela Tupou, Tolu Latu, James Slipper (capt). Reserves: Folau Fainga'a, Angus Bell, Allan Alaalatoa, Will Skelton, Lachlan Swinton, Tate McDermott, Lalakai Foketi, Tom Wright.

Australian Associated Press