McKenzie: What crisis?

Wallaby coach Ewen McKenzie put up a brave face in the wake of the latest injury setback, as they build towards the opening round of the Rugby Championship.

The Wallabies were forced into a second change on Tuesday - with Brumbies prop Scott Sio joining Waratahs hooker Tatafu Polota-Nau on the sidelines.

They were replaced in the squad by fellow Waratahs hooker Tolu Latu and Rebels tighthead Laurie Weeks.

Polota-Nau suffered a MCL injury in the Waratahs' historic Super Rugby Final victory at the weekend and will miss the opening Bledisloe Cup match, before being re-assessed for the return Test in Auckland.

Sio joined the squad on Monday, but suffered an ankle injury at training.  

The selection of Weeks continues his rapid rise in the Australian ranks, after the Melbourne prop made his debut for the Wallabies during the recent Test series against France.

Latu made his debut for the Waratahs this year and was a graduate of Australia's Under-20 program in 2012.  

He has shown plenty of raw potential and stepped up in the Super Rugby Final when teammate Polota-Nau left the field early in the second half.

Despite the latest setback McKenzie insisted there is no "crisis".

"We've got a number of very good players who are unavailable at the moment. That's just life, you get on with it," the Wallaby coach said.

"There's no crisis, that's just the way it is. I'm pretty excited to see how some of the guys step up."