Hackett is sidelined after suffering a knee injury during Wednesday night's FA Cup second-round replay win over Staines Town.
Reading loanee Henry was ineligible in midweek but would have missed out anyway with a hamstring problem.
But manager Kenny Jackett can welcome back another wideman in Dave Martin, who will be in the squad after missing the last two games with a groin strain.
Strikers Neil Harris (back) and Gary Alexander (heel) remain on the sidelines so Steve Morison will again start in attack.
Defenders Tony Craig (cheekbone), Zak Whitbread (hip), Scott Barron (ankle) and Pat O'Connor (cruciate) are still on the casualty list.