The former Cardiff player suffered an ankle injury during last weekend's goalless draw at Aston Villa and has been unable to train all week.
Head strong: Johnson has been ever-present this season
If Johnson is ruled out, Martin Jiranek is the obvious candidate to replace him providing he shakes off a thigh strain.
If Jiranek is also unfit, Liam Ridgewell would probably switch from left-back with Stuart Parnaby replacing him on the flank.
Provisional squad: Foster, Carr, Johnson, Dann, Ridgewell, Larsson, Ferguson, Gardner, Fahey, Hleb, Zigic, Taylor, Jiranek, Parnaby, Bowyer, Jerome, Phillips, Derbyshire, Michel, Beausejour.
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Explore more:People: Stuart Parnaby, Roger Johnson, Liam Ridgewell Places: Birmingham, Cardiff