Ward was named in Michael O'Neill's squad for the international double-header but has pulled out after feeling some tightness in his hamstring during the Rams' 2-1 npower Championship victory over Leicester at Pride Park on Saturday evening.
The 26-year-old has been hampered by hamstring problems for much of the season.
He has only recently returned from a three-month absence and was back in the starting line-up against the Foxes after a spasm against Crystal Palace at the start of March forced him to miss the away games at Cardiff and Birmingham.
"About an hour was all we could get out of Jamie on Saturday and he won't be right for the international games," Derby boss Nigel Clough told his club's official website.
"He felt his hamstring tighten a bit but he will stay with us for treatment and we hope he will be okay for Bristol City a week on Friday."
Aberdeen's Josh Magennis has been called up to take Ward's place in the Northern Ireland squad.