The eighth-placed Rabbitohs are undefeated in four games at the venue, where they play Brisbane on Friday night.
Walker was voted best on ground in NSW's 24-10 win over Queensland in game three of the series in Sydney.
"He will come back from his man-of-the-match performance in Origin on a high and that will put us in good stead," Souths legend Craig Coleman told AAP.
"Cody was outstanding for NSW but he has been outstanding the last two or three years. Ninety-five per cent of our attack is Cody."
The return of star fullback Latrell Mitchell from a calf injury has been delayed another week after he was ruled out on match eve.
The Rabbitohs get their NSW Origin quartet of Walker, Damien Cook, Cameron Murray and Keaon Koloamatangi back while returning centre Campbell Graham and forward Jai Arrow also missed the 36-32 loss to Canterbury in round 19 due to injury.
"They are pretty big ins for us," Demetriou said.
"Origin three from our perspective couldn't have gone better. Cam started for the first time at No.13 and was really impressive to watch and Cody controlled the game from start to finish.
"There is a lot of confidence with those guys. Keaon's (Origin) debut couldn't have gone much better for him."
Walker scored four tries at Sunshine Coast Stadium in a man-of-the-match display against the Warriors back in 2019.
"We are staying in the same hotel ... so hopefully that is an omen for tomorrow night," Demetriou said.
South Sydney are on 24 points and must start winning on a regular basis if they are to make the top four.Â
"You can't win the comp from outside the top four. Souths need to go on a run but they know that," Coleman said.
"With the players Souths have got they can do it, but we've lost five of the last seven.
"That is not good for your confidence but we will get confidence by having the big guns back."
