Israel Folau joined the main Wallabies training group briefly on Wednesday ahead of their Rugby World Cup semifinal against Argentina, but he remains under an injury cloud along with David Pocock and Scott Sio. The trio are pivotal to Australia's hopes of knocking out the rising power of world rugby, but their respective ankle, calf and elbow injuries are limiting their ability to prepare for the knockout fixture.

Pocock, whom the Wallabies missed badly in their tense quarterfinal victory over Scotland, was held back from running once again by coaching staff, and spent the session riding a bike. His inability to get onto the training paddock will surely test coach Michael Cheika's insistence that players must be fully fit to be picked to face the Pumas on Saturday.

David Pocock sat out training once again© Dan Mullan/Getty Images

Cheika had previously said that he thought Pocock would more than likely line up against Argentina, saying on Monday that "we know we've got the groundwork done so we don't need to push anyone; we just need to make sure everyone's right".

Sio, who suffered his right 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. Scans are understood to have revealed less damage than had been feared, but he still has substantial bruising on the elbow and there is little room for weakness in the physical engine room of the Wallabies' scrum.

The Wallabies insist they will give Sio every chance to prove his fitness but they enjoy good depth in the front-row, with Greg Holmes, James Slipper and Toby Smith available to step up.

Folau has been troubled since rolling his left ankle against England three weeks ago, but he lifted the hopes of Cheika and his staff by making a brief appearance during training at their south London base on Wednesday. He enjoyed a 10-minute stint running drills before leaving the field to continue his recovery.

Cheika was a surprise participant at training on Wednesday, packing 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 said last week.