Gardiner is currently battling ankle and Achilles ailments and has been reduced to stationary drills at team training.
"We're just being patient with that, and he may not be available for Round 1 … there's no point in rushing him, we've got other guys going well in those positions," Fagan said, via AFL.com.au's Michael Whiting.
"We'll just get him back into the team when he's ready."
Zorko, who recently surrendered Brisbane's captaincy, is expected to be available for the Lions' season opener, according to Fagan.
"We were half hopeful he would be right for the Geelong game, but he won't be," Fagan said.
"We're very confident he'll be available for round one.
"With an older player like him, we're not actually that concerned that he hasn't had that match practice, he's a natural touch player, he's very, very fit at the moment, so I'm happy for him to come into the season to play straightaway without any background matches.
"We're just using the time we've got rather than trying to rush."
Brisbane's clash with the Cats is set to take place on Thursday night, before it prepares for Ken Hinkley's Port Adelaide on March 18.