Scans have shown that Johnson's injury is not a major muscle tear and the influential central defender is expected to be back in time for the first leg of the play-off's should Blues qualify.
Luckily, manager Steve Bruce has plenty of cover at centre-back with new signing Olivier Tebily settling in very well, Darren Purse returning after serving a three game suspension and Steve Vickers now fit after injuries to both his knee and calf.