Mihocek hurt a pectoral muscle during the Magpies' 12-point defeat to Essendon at the MCG on Friday night.
Scans have revealed a rupture and he will have surgery within days.
"Brody is a resilient person and we have no doubt he and our high-performance team will be proactive in taking every step possible to ensure the best recovery," Collingwood's football manager Brendon Bolton said.
Magpies ruckman Darcy Cameron was also taken to hospital, for assessment on potentially broken ribs.
Defender Isaac Quaynor spent time off the field against the Bombers due to a toe issue and will be monitored during the week.
Collingwood (8-2-6) could drop out of the top eight by the end of the round, depending on other results, ahead of a crucial clash with Geelong on Friday night.
Mihocek will add to an injury list already containing fellow forwards Jamie Elliott, Beau McCreery, Mason Cox and Dan McStay.
"Brody looks like he's going to need surgery and he'll most likely be out for the season," Collingwood coach Craig McRae said after the match.
"As we always do, we love and support to get around our players and rally together."
After hurting his ACL at training in December, McStay is pushing for a return, likely to first be at VFL level.
"He's very close," McRae said of McStay. "Whether it's next week or the week, he's very close.Â
"Clearly after 'Checkers' (Mihocek) going out, we're probably going to need every one of our guys like Dan to be ready to present.
"But we're not going to rush Dan in before he's ready, because that doesn't make sense."
McRae was left frustrated by the loss against the Bombers, after Collingwood surged out to a 23-point lead late in the first quarter.
"It was hard to watch at times," he said. "There was a passage of some fairly unpredictable play for us.
"We have a strong DNA, as most teams do, and particular parts of that DNA were just not on show at times."
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