The Rabbitohs have come up empty-handed in 19 clashes with the Storm, while their coach Wayne Bennett hasn't tasted victory over rival Craig Bellamy since 2016.
But Bennett revealed on Thursday morning that Walker was out, forcing a reshuffle to the backline for the sell-out Anzac Day clash on Friday night at AAMI Park.
Jye Gray has been elevated from the bench to line up in the halves, while Latrell Mitchell remains at fullback.
Former St Helens halfback Lewis Dodd joins the bench in place of Gray, who had been starting in the No.1 jersey until this week when he made way for Mitchell.
"(Walker is) not playing. He's hurt his calf, got a severe tear there training two days ago, three days ago, so he'll be out for four or five weeks," Bennett said.
"Jye Gray will come in, and Latrell will be the captain.
"Five-eighth was his (Gray's) junior position. All his senior football has been at fullback, but I'm confident he can do the job for us.
"We're all disappointed, but (Walker is) most disappointed because it impacts on him personally, but nothing we can do about it."
Both teams are coming off ugly losses in round seven, with Souths outclassed by ladder-leading Canterbury 32-0 while Melbourne gave up a 14-point lead to fall to the Dolphins 42-22.
Bellamy said his team had responded well at training.
"It was disappointing to have 40 points put on us after we had a good lead ... but hopefully we can recover from that and play well this week," he said.
"Our completion rate has been a bit of a problem brushed under the carpet a little bit because we've been winning games but our completion rate has been really poor to be quite honest so that's something that's come into view this week."
Giant prop Nelson Asofa-Solomona has been cut from the match-day squad with Bellamy hinting he will need to build match fitness through the Storm's feeder sides after suffering concussion.
Melbourne welcome back centre Nick Meaney from a fractured cheekbone, while Sua Fa'alogo has been included on an extended bench and could replace winger Kane Bradley.
Meanwhile, Bellamy said there was no timeline for the return of athletic winger Will Warbrick, who continues to battle concussion symptoms after suffering a head knock in February.
He played in round one and then round four but hasn't been sighted since.
"To be quite honest, I don't really understand it, it's fairly complicated with the head knock which he got the head knock in the Indigenous and Maori game.
"I think he played a week or two after that and then he sort of had delayed symptoms and I'm not 100 per cent sure where it is ... it hasn't been great for us or for Will, obviously."
