Sio, who suffered his elbow injury during a collapsed scrum in the second half of Australia's great escape against Scotland on the weekend, remains the least likely to face Argentina.
Though scans earlier in the week are understood to have revealed less damage than initially feared, bruising is still going down on the elbow and in the physical engine room of the Wallabies' scrum there is little room for weakness.
The Wallabies insist they will give Sio every chance to prove his fitness and haven't entertained the thought of sending for an injury replacement - and enjoy good depth in the front row, with Greg Holmes, James Slipper and Toby Smith all available to step up.
Folau has been troubled since rolling his ankle against England three weeks ago, but lifted the hopes of Cheika and his staff by making a brief appearance during training at their south London base on Wednesday.
He had a ten-minute stint running drills before leaving the field to continue his recovery.
One surprise participant at training on Wednesday was coach Cheika, who packed down at flanker during scrummaging drills.
It is not an entirely unusual sight, however, with the hands-on Cheika keen to find any way to motivate his players.
"He gives the feeling that he'd like to be out there playing. He gets out there training with us," captain Stephen Moore told AAP last week.
- AAP
