The hosts were well beaten as the Cats flipped the script in the grand final rematch to win 17.15 (117) to 11.10 (76) on Thursday.
The veteran Zorko, boasting 311 appearances, was withdrawn after pulling up sore from last Friday's defeat of Carlton.
He missed two games with a calf injury earlier this year and coach Fagan said the former skipper - still an instrumental playmaker out of defence - would be treated with caution.
"He's 37, played 300 games," he said.
"We've gone from a Sunday to Saturday, to Friday to a Thursday game in the last month and sometimes it catches up to you.
"You've got to be careful with him ... it is a tough conversation, but you've got to be sensible."
Jarrod Berry (calf) was set to return against the Cats but didn't pass fit, while Noah Answerth (concussion) was missed as Shaun Mannagh kicked a career-high five goals.
Lincoln McCarthy (hamstring), who has been tried in a similar defensive role to Answerth this season was also out while Ty Gallop (hamstring) missed the clash too.
"We've got 10 days, which I feel like we need," Fagan said of the preparation before they face GWS in Sydney.
"We need to suck a bit of air in, have a little rest and get ready to go again.
"I'm not that quick to press the panic button.Â
"Some things weren't good tonight, but need to have a look at the vision and decide whether they are a real concern or not."
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