Strikers Evans (collarbone) and Ward and midfielder Williamson (both hamstring) were all forced off in the midweek defeat at Peterborough and will be sidelined for several weeks.
But manager Kevin Blackwell will be boosted by the return from suspension of forward Darius Henderson and could recall Henri Camara to his starting line-up, with Mark Yeates or Stephen Quinn stepping in for Williamson.
Blackwell has no other new injury or suspension problems as his side look to get their play-off push back on track after back-to-back defeats, but long-term absentees Gary Naysmith, Ryan France (both knee) and Derek Geary (ankle) remain sidelined.
