Graham went under the knife in February to try and heal his problematic sternum, after it had been a lingering problem throughout 2023.
It had initially been expected Graham would miss the first half of the NRL season, before his return date was revised to round 18.
But the 25-year-old is still yet to resume training with Rabbitohs teammates, and the club now believe he may not return at all this year.
As things stand, it is possible the Rabbitohs would only consider bringing him back if they remain a finals hope late in the season.
Tyrone Munro may also be out of action for the rest of the year after his collarbone woes. (Mark Evans/AAP PHOTOS)
Graham is not alone in his plight.
Winger Tyrone Munro may also not play again this year, as he attempts to come back from a second collarbone injury.
"Campbell hasn't been training with us at all. He hasn't touched a ball," interim coach Ben Hornby said.
"He's still a long way off, if at all.
"Tyrone is the same. At the moment, there's no return date for either of those guys.Â
"They could be back in four or five weeks, but the likelihood is they won't come back this year."
Graham's situation is a potential blow in the Rabbitohs' finals charge, which is now alive and well after their 14-0 victory over Manly marked their fourth straight win.
Prop Tevita Tatola is also now out for the season, joining Lachlan Ilias in having his year ruined by injury.
Fellow front-rower Shaquai Mitchell is expected to miss another month, as is second-rower Jacob Host.
Centre Isaiah Tass is also still some way off returning from an ankle injury.
Given the Rabbitohs inferior for-and-against, it's likely Souths would need to win eight of their last 10 to make the finals.
But they refuse to be drawn into talk around top eight, after spending the first 11 rounds of the season at the bottom of the ladder with coach Jason Demetriou sacked.
"I'm being honest when I say all I am worried about is next week, and making sure we prepare the best we can every week," Hornby said.
"We have good enough players to win games. That will take care of itself if we do the right things off the field and on the field.
"I still don't think we're playing unbelievably. I still think we've got more in us. We still have things to work on and improve.
"If we just keep doing that and take the results out of our equation, the results will happen."
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