Leadbitter was booked for the 10th time this season during Monday’s 2-0 defeat at Watford and will sit out the home games against the Millers and Wolves as a result, robbing head coach Aitor Karanka of one of his most influential players as the season approaches its climax.
Fellow midfielder Adam Clayton could join him if he is cautioned this weekend ahead of Sunday’s cut-off having reached nine yellow cards against Wigan on Good Friday.
Daniel Ayala remains a doubt with a thigh problem, while fellow central defender Kenneth Omeruo is nursing a groin strain and has not figured since his return from international duty with Nigeria. Damia Abella (knee) and utility-man Rhys Williams (Achilles) remain on the sidelines with the latter looking at next season for a return to action.
Rotherham boss Steve Evans could name an unchanged side for their first-ever league trip to the Riverside.
The Millers ended a four-game losing streak by registering a vital win over Brighton on Monday, easing their relegation fears in the process, and Evans could name the same team.
Skipper Craig Morgan is still banned while defender Frazer Richardson is unlikely to play again this season due to a calf injury.
Midfielder Lee Frecklington and striker Danny Ward will hope to earn starts and Richard Wood is in contention after his recall from Crawley.