South Sydney remain confident they can secure an unlikely finals berth despite losing inspirational skipper Roy Asotasi for the rest of the NRL season.

The New Zealand international will require surgery after damaging the anterior cruciate ligament in his right knee in the Rabbitohs' surprise 36-22 win over reigning premiers Manly on Saturday night.

He will be out for at least six months, also ruling him out of New Zealand's Four Nations campaign in England in November.

Asotasi's recent form had provided the backbone for Souths' late-season revival, with four wins from their last five matches putting them just a point outside the top eight.

But the Bunnies believe they can continue to build momentum even without Asotasi, and now plan to use his injury as another motivating factor in their season.

"It's a massive loss, he's our captain and one of our best players," five-eighth John Sutton said.

"Losing him, it's going to be tough for us each week but I think the boys are going to have to dig deeper and we can keep winning.

"It was a bit of a shock, but we're all just going to have to train harder.

"It gives us even more to play for now because we can do it for him."

Sutton said he was confident the Rabbitohs had enough depth in their forwards to cover for the loss and singled out mid-season recruit Michael Crocker as the man who could step up in Asotasi's absence.

"We've got a good bunch of forwards and I think Mick Crocker is going to be even more vital to us now," Sutton said.

"He's one of those experienced leaders in the forwards.

"But we've all go to really come out firing, without Roy's go-forward we would have been struggling in games this year, so I think everyone's going to have to step up."

Souths have a tough run home with matches against Gold Coast, Penrith, St George Illawarra and Cronulla, three of which they will likely need to win to make the top eight.

But Sutton said the side could not get caught up in the mathematics just yet.

"I think if we just keep winning, then we'll be talking finals," Sutton said.

"If we keep winning week in week out hopefully we'll be there."

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