Matt Faessler, fresh from becoming the first Wallabies' hooker to score a hat-trick of tries in a Test in the thrashing of Wales last Sunday, has succumbed to a calf injury since being named in the starting XV on Friday.
The loss of the outstanding Queensland No.2 means Australia's strength in depth will be again tested, with Western Force's Brandon Paenga-Amosa stepping up for his first Test start in three years, while Brumbies' youngster Billy Pollard replaces him on the bench.
Reds' Josh Nasser will then join up with the squad for the final week of the tour in Ireland.
Faessler is suffering from a calf problem and will miss the Murrayfield clash. (Jono Searle/AAP PHOTOS)
The bad news was compounded when any chance of a meaningful final session on the eve of the clash at Murrayfield was scuppered as the snow that came at the end of the week's Arctic blast blocked the team bus and prevented them getting to the training ground.
Waking up to a snow-hit city put the tin hat on a disrupted week's build-up ever since the victory over Wales in Cardiff last Sunday, their second win in the hunt for the British Isles grand slam.
Frozen pitches had also forced other sessions to be cancelled or amended earlier in the week.
Coach Joe Schmidt was left "massively appreciative" that the Scottish Rugby Union had allowed the team to train at undersoil-heated Murrayfield itself on Friday, while the team's kickers also later got the chance to practice there on Saturday afternoon.
But the main squad only had chance to walk through some key drills indoors.
"I've not trained in the snow before. I know a few of the boys from Europe or who've played in the UK have but it's quite exciting to get out here for the captain's run and have a little run around. It'll be cool," said skipper Harry Wilson before the session had to be cancelled.
Even though temperatures were set to rise for Sunday's (Monday AEDT) match itself, It was certainly not the way the Wallabies would have wanted to go into a Test against a side most of their players believe will provide them with their sternest examination yet on tour.
Though he had a brilliant record against the Scots when coach of Ireland, Schmidt reckons Gregor Townsend's current side may be just about as strong a Scotland side as he's seen.
"The balance they have across the board is really impressive. Right through, from their from their tight five, a really good back row, and I'd have seen a lot of Finn (Russell) over the years," said Schmidt.
"A lot of their players are hitting that sweet spot of being between 25 and 30 and having 30 to 60 caps, where they've got enough maturity and experience to have the right amount of confidence to be able to adapt the game as it needs to be done.
"And they've some really good strike players, Blair Kinghorn, both wingers - Duhan van der Merwe has obviously been a standout but Darcy Graham's been electric too - and through midfield, Sione (Tuipulotu) is pretty well known to our boys, obviously, and Huw Jones is elusive and brings a real experience to the midfield.
"Pretty hard to pinpoint a weakness."
