Sidoli will be out for around eight weeks having torn ligaments in his elbow which requires surgery. Fellow lock Scott Morgan dislocated his elbow in the Musgrave Park clash, and will be out of action for four to six weeks.
Centre Ashley Smith hurt his shoulder in the first half which will confine him to the sidelines for the next month.
Martyn Thomas and Will Harries were initially injury doubts but seem likely to overcome hamstring trouble in time for Sunday's game, whilst the calf injury which forced Wayne Evans off the field in Cork should not affect his availability for the game.
The Dragons beat Gloucester in the group stage of the competition in November 18 v 12 at Rodney Parade but Gloucester have climbed up to third in the English Premiership in recent weeks and are on a nine-match winning streak.