Slipper started in all four Bledisloe Cup tests as coach Dave Rennie's first-choice loosehead prop, but the Brumbies star suffered a dislocated elbow late in the first half of the Wallabies' last-start 24-22 win over the All Blacks.
The painful injury created a two-man race for the No 1 jersey between Slipper's Brumbies team-mate Sio and one-cap Waratah Angus Bell.
Bell showed he is more than capable of making the step up to international rugby when he replaced Slipper at Suncorp Stadium, but Rennie has opted for the safety of 66-test prop Sio for the key Argentina clash.
If Argentina hand the Wallabies their second loss of the Tri-Nations campaign, the Pumas will have one hand on the trophy. But an Australia win – followed by a bounce back from the All Blacks on Saturday week – will set up a tournament decider at Bankwest Stadium on December 5.
With the stakes high, Rennie has not made a single change to his starting back line.
James O'Connor's latest injury setback means Reece Hodge will retain the No.10 jersey.
The Rebels star will continue to build his partnership with Nic White in the halves.
Young guns Hunter Paisami and Jordan Petaia have been given another opportunity to build on their centre combination.
The Pumas clash will be Paisami's second senior game – at club, Super Rugby or test level – lining up at inside-centre. The first came last Saturday against the All Blacks.
After the thrilling win, Paisami hopes he's found a home in the position.
"It's actually fun. I was just saying to Jordy [Petaia] I think I like it more than 13," Paisami told the Sydney Morning Herald.
"You don't have to run as many hard lines. You can ball play a bit more and save your body a bit more at 12. But I enjoyed it.
"I played 12 when I was young, at school, but I never even played it at [Queensland Premier rugby club] Wests. I was always 13 at Wests."
While he may be inexperienced at the critical playmaking position, Paisami has enjoyed having the ball in his hands more often.
"I can get more early ball and I like playing flat as well," he said. "Receiving those quick balls off Rabs, Hodgey or Noah at 10, I enjoy that."
Rennie has since asked Paisami to work on his decision-making and communication skills, which are key to any inside-centre's game.
"I hardly talk," he said. "Even during team meetings or units or on the field.
"For me to improve and to grow my game, I have to get out of my comfort zone and chat more. I reckon I've improved through the weeks I've been at 12, but I reckon I still have a lot to learn."
Tom Wright's stellar debut has seen him keep his spot on the wing alongside Marika Koroibete and Tom Banks in the back three.
Rennie will reveal the remainder of his side on Thursday afternoon.