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The Power responded to a dismal effort against West Coast in round two with a brave start against the Cats on Sunday, but conceded four goals late in the second quarter and trailed by 30 points at half time.
The visitors were less competitive in the second half, eventually going down by 79 points.
Primus was again forced to question the work rate of his on-ballers, who were beaten around the stoppages and criticised for not applying enough defensive pressure.
Mitch Banner travelled with the team to Skilled Stadium as an emergency and could add much-needed grunt to the midfield, while forward Brett Ebert and defender Jacob Surjan performed well for Port Magpies on Saturday.
Steven Salopek sat out the loss to Geelong with a hamstring complaint, but has been cleared to play against the Crows.
Cassisi said the club wouldn't tolerate players that failed to work hard across four quarters.
"[Our work-rate] definitely can be questioned again in that second half. I think Geelong's midfield worked a lot harder than ours and we need to address that," Cassisi said on Monday.
"There's no doubt there could be some changes this week. If the match committee are going to make some changes it's got to be the guys that aren't sticking to our structures and aren't giving us the output we require with their effort.
"If anyone falls into that category there's a fair chance they won't play this weekend. We just need to stick to our selection process and try and find a mix of guys that are going to deliver for us on game day."
It was always going to be a tough start for the winless Power this season with matches against the premiers of the last two years, Collingwood and Geelong, away from home in the opening three rounds.
However, the club expects to be more competitive and Cassisi said it was the nature of his side's losses that had been the most concerning.
"You can handle losing, maybe, due to a lack of skill or just being fairly beaten, but when it's your effort, intensity and desperation being questioned that's when it does get pretty serious," he said.
"Our structures do hold up when we are doing things right, but we need to do it for a longer period of time … and I expect to see nothing less than a desperate effort from our 22 guys this Saturday night."
Cassisi watched the Power's clash with the Cats from his lounge room, after having surgery to repair minor cartilage damage in his knee but will be on hand to address the midfielders during the breaks at AAMI Stadium this weekend.
Port Adelaide has won four of its last five games against Adelaide, including a 19-point win in round 17 last season to end a nine-game losing streak.
The Crows, who have claimed one win from two starts this season, will start warm favourites in Showdown XXX, but Cassisi was hopeful his side could spring another upset.
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"You can't rest on it, but in the past Showdowns have showed that it doesn't matter where you are on the ladder, or what your win-loss record is [the games] are always an even show," he said.
"I think form counts for nothing, but we do need to turn things around in certain areas."
