Lolesio was stretchered off wearing a neck brace, and in apparent extreme pain, midway through the first half of his Brumbies' 33-14 derby win over the Western Force in Perth.
The Brumbies' and incumbent Australian No.10 was twisted in an accidental off-the-ball play while trying to repel a Force attack on his goal line in the 20th minute of Saturday night's derby.
It was initially unclear if Lolesio had suffered a back, hip or leg injury in the incident.
But Stan Sport's sideline commentator and former Wallabies star Cameron Shepherd said Lolesio had sustained a spinal injury.
"We don't want to speculate too much at the moment because there's a lot of scans and a lot of checks that need to be done," Shepherd said.
"But the one small bit of good news is that he is moving his arms and legs.
"They have confirmed it is a spinal injury. At the moment, we just don't understand the severity.
"But, fingers crossed, moving his arms and legs is obviously a very, very good sign."
Two-time World Cup-winning Wallabies legend Tim Horan added: "It wasn't a great sign that he was holding the green whistle. That shows he was in a lot of pain."
Lolesio's injury occurred almost exactly 24 hours after fellow Wallabies star Joseph-Aukuso Suaalii was escorted off the field, also on a medicab and in a neck brace, during another Australian derby between his NSW Waratahs and the Queensland Reds in Sydney.
Suaalii was knocked out after copping an accidental knee to the head from his Waratahs and Wallabies teammate Andrew Kellaway.
Waratahs coach Dan McKellar said post-match Suaalii went home with his parents in a "groggy" concussed state.
Concerned Wallabies coach Joe Schmidt was also watching on at Allianz Stadium.
While Schmidt's openly known policy is to not select overseas-bound Wallabies players, Lolesio's injury ahead of his move to Japan at season's end could prove another potential huge blow ahead of Australia's hosting of the British and Irish Lions for a three-Test series this winter.
In a pivotal and seesawing encounter, the Brumbies were elated to jag a bonus point after fulltime when replacement hooker Liam Bowron touched down.
The bonus point vaulted the Brumbies above the Crusaders into second spot in pursuit of a top-three finish to guarantee a home playoff.
"It's so important," said Brumbies forward Tom Hooper.
"We knew we couldn't put the gun in the holster and we needed to keep playing and it was great."
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