Mitchell was slated to return from a nine-week layoff with a calf injury at Sunshine Coast Stadium on Friday night, but coach Jason Demetriou told the Sydney Morning Herald he would be given another week to recover.
"Latrell won't play," Demetriou said.
"He hasn't trained with the team a lot, and he only had the one full session with the team on Tuesday. There's no pressure from us for him to play this weekend. We want him right.
"The performance staff would rather him get through another week of training. He'll definitely be back next week."
Blake Taafe will play fullback while Tallis Duncan has been named on the bench.
Broncos coach Kevin Walters said he was looking forward to the return of Walsh, who has not played since the round 17 loss to the Gold Coast.
"Both teams are primed and ready to go with some of the best players in the game in both sides. It shapes as a great clash," Walters said.
"We are not expecting too much from Reece except what he brings to our side ... a lot of confidence, good speed and he defends well.
"If he can bring that, then that is a good starting block.
"Keep in mind he has missed the last month of footy but it is great having him back in a Broncos jersey."
The Rabbitohs have strike power across the park, with Mitchell only one cog in what can be a well-oiled machine. Even though he's out, the Broncos must be switched on.
"Defence has been a big focus for us this week, and not just for one player," Walters said.
"We need to be strong with our line speed, aggressive, and do all the little things well.
"Our attack can help us as well if we can build scoreboard pressure."
The Broncos are in second position on 30 points, while the Rabbitohs sit eighth on 24.
Brisbane have NSW prop Payne Haas and Queensland lock Patrick Carrigan returning from injury.
Haas, off contract at the end of 2024, will test the open market from November 1 but Walters said the Broncos remained confident of keeping him.
"Payne belongs here at the Broncos and we will make sure he is accommodated," Walters said.
"We are respectful of his decision to have a look around but we know he is going to be a Bronco for life.
"We will work with him and his manager to sort out something that is going to be great for both."
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