The Cats ruled Christensen out on Friday morning after he missed Thursday’s main session with flu-like symptoms.
Christensen has been replaced by second-year midfielder Brad Hartman, while defender Mitch Brown has been upgraded to the Cats' emergencies list.
The emerging onballer was just starting to find his feet, having missed the first 12 games of the season following back surgery in February.
Mathew Stokes returns from the ankle injury he sustained in the club's 40-point loss to Gold Coast in round 14, while Dawson Simpson has also been recalled to combat the effectiveness of Giants ruckman Shane Mumford.
The Cats have rested 198cm utility Mark Blicavs.
Geelong departs for Sydney on Friday afternoon.
