Top-scorer Harris is still sidelined with a back injury and fellow striker Alexander has been ruled out until the new year with a heel problem.
On-loan Reading winger James Henry, who has been struggling with a hamstring injury, does not have permission to play in the competition.
Jackett also has problems in defence with Jack Smith sustaining a knock during Tuesday night's draw at Exeter.
Fellow defenders Tony Craig (cheekbone), Zak Whitbread (hip), Scott Barron (ankle) and Pat O'Connor (cruciate) are still on the sidelines.
Midfielder Ali Fuseini could start after returning from a knee injury on the bench in midweek.