Here's what you need to know about Kaleb Johnson's fantasy value as a Packer:
The big picture: Johnson was traded from Pittsburgh to Green Bay on Aug 30 — directly because Josh Jacobs was placed on the Commissioner's Exempt List the same day. So he's a contingency play pure and simple. (from the Kaleb Johnson page)
The bad news: His rookie year in Pittsburgh was rough — he averaged just 2.46 yards per carry and was third-string behind Lew Nichols and Travis Homer heading into Year 2. One trade grade called it a C for the Packers and noted "the odds are decent that they just lit a pick on fire."
The opportunity: If Jacobs misses extended time, MarShawn Lloyd is the primary beneficiary, not Johnson. Johnson is competing with Chris Brooks for backup work. He's a big, physical runner with pass-protection ability, so he could carve out a role — but he'd need Lloyd to miss time and show real improvement to be fantasy-relevant.
Bottom line: Johnson is a deep stash / handcuff's handcuff right now. He's one Josh Jacobs absence + one MarShawn Lloyd absence away from significant opportunity. Not worth a roster spot in standard leagues unless you're in deep formats and betting on the Packers' RB room getting thinner.