Ward, who has netted 12 goals this season despite missing chunks of the campaign with a troublesome hamstring problem, missed the last-gasp draw at Barnsley with an ankle injury while Bryson was also absent on Tuesday night.
Bryson was left out of the squad as back-to-back games in the space of four days would have proved too much for the 26-year-old, who continues to play through the pain of a groin complaint.
Rams boss Nigel Clough will give the duo as long as possible before making a final decision on their fitness.
Teenage striker Mason Bennett impressed during the 1-1 draw at Oakwell, in what was only the 16-year-old's third start in professional football, giving Clough a tough decision to make on whether to stick with the Academy product or recall Conor Sammon.
Derby will be looking for a first win in four matches against a Posh team who are unbeaten in their last 10 Championship outings.