Cheika: Sio is my back-up hooker
Cheika picked veteran Stephen Moore as one, and the injury-prone Tatafu Polot-Nau and the second hooker with no able replacement if one of them goes down.
The Wallaby coach has hit back declaring that prop forward Scott Sio will perform hooking duties as the third option if needs be.
Critics see it as a risk and a gamble, but Cheika said plenty of thought had gone into the call between him and scrum coach Mario Ledesma.
"We know that Scott Sio will be the back-up – he's played hooker before. He's got a good lineout throw and he's a very strong scrummager in that position," Cheika said.
"We've been practising for a while now and I wouldn't be making those types of decisions without knowing that the person could do the job."
Sio has played hooker at schoolboy and Under-20 level, and at 115kg and 1.87m, he is well equipped to play at hooker.
James Hanson is on standby for the Wallabies, and would come into the squad if Polota-Nau or Moore suffered a tournament-ending injury.
"If we get something short term, then Sio's got experience and he's more than capable of covering that void," Cheika said.
Sio has been working under the guidance of Wallabies scrum coach and four-time World Cup hooker Ledesma, and Moore has been impressed by his Brumbies teammate.
"He's been doing a lot of practice at training. I told him not to get too good at it, but he's been really good so far," Moore said.
"I'm sure when the coaches were picking the squad, they factored everything into that [decision]."
Moore was delighted to see so many Wallabies fans cheering the side that was announced.
"We've been tucked away training hard over the last couple of weeks and it's terrific to get out and see the public," Moore said.
Cheika said the public farewell hit home, and he suddenly realised that the World Cup was just around the corner and what it meant to the people.
"Today has been a bit of an eye opener for me because, when you're in the training part of it all, you're closed in and you've got your head down and working," Cheika said.
"When you've got a chance to get out amongst the supporters and because it's a World Cup, you cross over all the code's supporters. There's been so much genuine support for us and it feels really good."
The Wallabies leave Sydney for Chicago on Saturday, August 29, and play the United States in a warm-up match on September 5, before tackling Fiji in their World Cup opener in Cardiff, on September 23.
Moore said training continued to ramp up as they prepared for northern hemisphere-style rugby.
"Set-piece wise, we've been doing a lot of scrummaging. We know that's going to be so important, and also a lot of mauling. Those two things are going to be so important," he said.
"We're not looking too far ahead, we are just looking at that first game against Fiji.
"The first game is so important. To win that and play our best footy early, is going to give the team a lot of confidence."
