Knight would have returned to the first grade side against Newcastle this Friday had he not been targeted by Parramatta's Solomone Naiduki in a cannonball tackle - an illegal move where a player's legs are taken out from behind as he is being held upright by another defender.

The tackle poses serious risk of knee injury and was outlawed by the NRL ahead of the 2014 season.

But prohibiting the cannonball tackle has not eliminated it entirely and the NRL has not always enforced its ban with suspensions. Trent Loiero and Lindsay Collins were cited for cannonball tackles earlier this season but both escaped with fines.

Demetriou said Naiduki's three-week suspension was not an adequate punishment, given the nature of the tackle and the severity of Knight's injury.

"There's no accident in that. It's a deliberate act. There's intent," Demetriou said.

"I played the game for a long time, since I was six years old, and never once did I look at a bloke's knees and cannonball him. It's something our game needs to get rid of.

"(Naiduki) misses 10 minutes (in the sin bin) and three weeks and we've got a guy who's out for the season for an act that can be ruled out of our game so easily."

Demetriou said the tackle left Knight "distraught".

"That's the thing we're not taking into account with these types of tackles, there's an emotional toll that the player who gets injured has to take on," he said.

"It's left up to us to help Liam get through this."

Knight's ACL tear was the worst injury on a busy weekend for the Rabbitohs' medical staff.

Campbell Graham (facial fracture), Hame Sele (hamstring) and Mark Nicholls (concussion) will miss the clash with Newcastle, as will State of Origin representatives Damien Cook and Cameron Murray.

While Demetriou said the long list of outs was frustrating, he was pleased fringe first-graders Michael Chee Kam, Davvy Moale, Blake Taaffe and Jed Cartwright would have the chance to come into the side.

"We're really confident that the team we've got will go out there and put a performance in against Newcastle," he said.

Star fullback Latrell Mitchell and winger Alex Johnston wore strapping on their upper legs at training on Thursday and spent time away from the team consulting with head physiotherapist Eddie Farah.

But Demetriou said neither was in doubt for the game against the Knights.

"We're in round 17, bodies are busted a bit," he said.

In the absence of Nicholls, Daniel Saluka-Fifita will make his club debut just four days after being granted an early release from his contract with the Sydney Roosters.

Australian Associated Press