Wallabies lineout caller Rob Simmons has backed Test rookie Nathan Charles to to hold the set piece together for the opening Bledisloe Cup clash after Tatafu Polota-Nau was ruled out with a knee injury.

Polota-Nau, who limped off just after halftime in NSW’s historic 33-32 Super Rugby final win over the Crusaders, underwent scans on Monday and was diagnosed with a low-grade MCL knee injury.

With first-choice rake Stephen Moore already out for the season with a knee injury, the Wallabies will need to rely on their third-choice hooker when they host the All Blacks for the opening Bledisloe Cup match in Sydney on August 16 – and possibly for game two in Auckland just one week later.

The man looming to fill the void is Western Force hooker Charles, who earned his first two Test caps off the bench against France in Moore’s absence earlier this year.

Simmons said while the Wallabies would miss both Moore and Polota-Nau around the field, they wouldn’t lose much in Charles – especially at the lineout and scrum.

“It’s not going to step down that much. He’s very good at set piece time,” Simmons said.

“My opinion is that’s one of the reasons he’s been picked.

“Hopefully he gets his head around what this game plan’s about and he’ll contribute to the team just as well as anyone.”

While Bledisloe clashes are always a huge occasion, there will be extra incentive for both sides to get one over their trans-Tasman rivals as the All Blacks will be gunning for a tier-one record 18th successive Test win.

The Kiwis have a crucial injury concern of their own, however, with champion playmaker Dan Carter set to miss the first four weeks of the Rugby Championship after cracking his upper fibula.