The Wales midfielder was given his marching orders during the 3-1 defeat against Sheffield Wednesday at the weekend having been shown his second yellow card in the 72nd minute, a dismissal which carries an automatic one-match suspension.
Manager Dave Jones cut a frustrated figure after the defeat and he is pondering changes ahead of the visit of Nigel Clough's side.
The Bluebirds boss has grown tired of his side's inconsistency this season and after Saturday's loss, the club's fifth in their last six games, accused some of his players of switching off.
With Ledley ruled out, Jones has at least been boosted by the timely return from suspension of fellow midfielder Stephen McPhail.
Forward Ross McCormack is hoping to make a comeback from his hamstring injury after the forthcoming international break while full-back Kevin McNaughton (ankle) is also close to a return but needs to first build up his fitness. Kelvin Etuhu (ankle) is out until around the end of November.
Meanwhile, Kris Commons is a doubt for Derby's trip to the Welsh capital
The forward missed the weekend defeat of Bristol City after sustaining a hamstring a problem in training on Friday and boss Nigel Clough is unsure whether he will recover sufficiently to be included in the squad.
One player definitely out is Stephen Pearson (groin). The midfielder also missed the game against the Robins with an injury sustained in training last week. Scans have revealed a slight tear that will keep him sidelined for around a month.
Captain Paul Connolly finished Saturday's match despite carrying a foot injury and Clough will hope he is fit enough to continue at full-back.
Dean Leacock could be rested after making only his second start in 10 months following a serious knee injury against City and Miles Addison may return to partner Shaun Barker at the heart of the defence.