The forward has made only four appearances for the Robins following a bout of illness and he has little chance of adding to that tally this weekend after suffering a groin injury.
Chris Iwelumo could be making his last appearance for City as his loan from Wolves nears its conclusion, although the Robins are hopeful of extending the striker's stay at Ashton Gate.
Johnson could be boosted by the return of Jamie McAllister after he continued his comeback from a calf strain in a County Cup win over Bristol Rovers in midweek.
Brian Wilson also played in the 3-1 triumph, although Saturday's game is set to come too soon for the midfielder. Evander Sno, Marvin Elliott and Jamie McCombe will also miss out.