The Wallabies will sweat on the fitness of a battered Scott Sio as the scrum turns to some Argentinian knowledge to find its feet again for their World Cup semi-final clash. 
Former Argentina hooker "Super" Mario Ledesma looms as the Wallabies' trump card as he attempts to be the architect of his countrymen's demise in his role as Australia's scrum coach.
But the Wallabies' first concern is whether Sio has suffered a serious elbow injury and whether star duo Israel Folau (ankle) and David Pocock (calf) will be fit to play against Argentina at Twickenham on Sunday (Monday morning AEDT).
Sio was forced to leave the field in the second half after a scrum collapsed on his right arm in Australia's last-gasp 35-34 win against Scotland.The scrum struggled to gain the upper hand against Scotland, conceding three penalties and failing to maintain the high set-piece standards they demonstrated against England and Wales.
That's where 84-Test Argentina hooker Ledesma will be called into action. He has been credited with the scrum transformation from pushovers to a respected pack and the Wallabies will need his magic.
"It [the scrum] was a bit inconsistent," said captain Stephen Moore. "I thought Scotland scrummaged really well but there were certainly some things we can work on."
The Wallabies forced just three turnovers against Scotland. Pocock had forced 10 in his three games.
"The guys who stepped in [against Scotland] did a fantastic job," Moore said. "A guy like David, he's a very special player. When he's not playing in any team ... he brings so much to the game that you're certainly going to miss that."