Suns forward Humphrey has been suspended for two matches, ruling him out of clashes with Melbourne and Sydney after this week's bye.
Gun recruit Petracca (hamstring) is also sidelined, and with Brownlow Medal winner Matt Rowell (finger) still unavailable, coach Damien Hardwick has significant holes to fill in his engine room and forward line.
The challenges come with ladder leaders Gold Coast (3-0) looking to extend their winning start to the season.
Humphrey pleaded not guilty to his rough conduct charge, arguing his sling tackle on Richmond's Maurice Rioli was not unreasonable or dangerous.
He also argued against the AFL match review officer's "high impact" grading, with the tackle also assessed as careless conduct and high contact.
In his evidence, Humphrey suggested Rioli's movement and force put him off balance and affected the tackle, leading to the 360-degree motion.
Suns advocate Adrian Anderson said Rioli's free arms "cushioned the blow significantly" and limited the potential to cause injury.
But the AFL argued Humphrey breached the duty of care owed to Rioli by slinging him to ground with "excessive force".
The tribunal agreed and upheld the ban, which is the first of Humphrey's 65-game career.
"There is a point about halfway through the tackle when Humphrey accelerates the momentum and the rotation, and slings Rioli with considerable force in turn," the jury found.
"While Humphrey knew that Rioli had both arms free, he should also have known or assumed that having both arms free in a tackle of this type - with full rotation and a high velocity sling - would likely be of limited assistance in reducing the impact."
Richmond's medical report stated Rioli had a sore neck and was treated for whiplash, but did not have any concussion symptoms.
The tribunal threw out Anderson's suggestion that Rioli's whiplash was caused by a separate incident later in the match.
"The wording of the medical report does not permit this conclusion," the jury found.
Humphrey missing Gold Coast's next outing adds another thread to the game against Melbourne, who were among several Victorian clubs who courted the young forward during last year's trade period.
The round-four fixture had been billed as a 'grudge match' between the Demons and Petracca, a 2021 premiership hero who left the club for greener pastures at the end of last season.
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