McArdle received a second half booking at London Road for a foul on Peterborough's Lee Tomlin - his fifth caution of the season - meaning the Northern Ireland international will have to serve out a one-match ban for the Rotherham game.
McArdle's absence will now most likely leave at least one of the trio of Matt Taylor, Carl McHugh and Luke Oliver in line for a spot in City's opening eleven to face Steve Evans' Millers.
Speaking about the McArdle suspension, Bantams boss Phil Parkinson said: "Suspensions and injuries happen, especially at this time of year, and we will have to deal with it.
"Whoever comes in now will have to step up to the plate, like Andy (Gray) did today (at Peterborough United).
"I am a bit disappointed on the McArdle booking though.
"I went to see the referee before the match and asked if he could ref the game with some understanding and common sense because players from both sides were coming into the game on three and four bookings.
"Rory has got the ball for the tackle that got him his booking. It was also his first real tackle of that nature in the game, so I felt to get a booking was harsh."