Already sidelined for the rest of the AFL season, Petracca was admitted to hospital on Saturday night with appendicitis.
The 28-year-old appeared in good spirits, with his girlfriend Bella Beischer posting a photo of the premiership star in hospital with the caption "still smiling".
The Demons indicated the illness is unrelated to the spleen, lung and rib injuries Petracca sustained in the on-field collision that put him out of action last month.
"Christian experienced increased abdominal pain yesterday and was admitted to hospital, where he was diagnosed with appendicitis," Demons football manager Alan Richardson said in a statement on Sunday.
"As a result he will undergo surgery today (Sunday) to remove his appendix.
"It is obviously a very stressful time for Christian, Bella and their families, who have already been through so much over the past month, and our focus is on providing them with as much love and support as possible.
"It is testament to Christian's character that he continues to navigate these traumatic challenges with such a positive attitude."
Petracca has sidelined since Melbourne's loss to Collingwood on June 10, when he was crunched by an accidental knee from Magpies captain Darcy Moore.
Petracca suffered a lacerated spleen, punctured lung and four broken ribs from the collision.
The Demons were criticised for letting the prolific midfielder back onto the field that day but fiercely defended their medical staff in the aftermath.
Petracca and coach Simon Goodwin both publicly went in to bat for club doctors, who were cleared of any wrongdoing by the AFL'.
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