Warriors assistant coach Andrew McFadden was optimistic that Lillyman, who injured his ankle in the 20-18 defeat of North Queensland last weekend, would be available on Sunday.
"We're still hopeful he'll come good," he said.
McFadden said Russell Packer, who has been out with a bicep problem, was a possibility to get his first run of the year if Lillyman was scratched.
Three other players failed to last the win over the Cowboys - fullback Kevin Locke, centre Dane Nielsen and utility Ben Henry.
Nielsen received rib cartilage damage and McFadden said his chances of facing the Rabbitohs were 50-50.
With Jerome Ropati being given more time in his return from a serious knee injury, 19-year-old Ngani Laumape is being lined up as replacement if Nielsen is unavailable.
"He's a fearless young kid," McFadden said of Laumape.
"I'm sure that, given the opportunity, he will take it with both hands."
Usually a centre, Laumape made his NRL debut last month on the wing and has impressed in his two appearances there.
However, he makes way on the wing with the return of Vatuvei from an ankle injury.
Locke and Henry both received head knocks, with Henry unlikely to be available this weekend.
The news on Locke, who watched on at training on Thursday, was more favourable.
"Kevin looks like he'll be in the team," McFadden said.
"He's just had another day off today, just to get himself feeling a little better."
McFadden said the Warriors' injury list, which runs to double figures, was just part of the game.
"We don't see these as distractions," he said.
"They're just things that happen every week in rugby league. It's a tough game and someone could fall over at training there today and it's just a case of he's out and you're in."