King reported neck pain after the Kangaroos' win over Brisbane last weekend and stayed in Queensland for medical examination.
It revealed a disc injury near the 25-year-old's spinal cord.
King had surgery to fuse the C5 and C6 vertebrae in her neck and is recovering in Brisbane.
The midfielder is expected to return to action in 2027, with the club's focus on supporting her through a long rehabilitation period.
"We wrap our arms around Mia," North Melbourne women's football manager Erin Lorenzini said in a statement.
"We are devastated for her, but also full of admiration for how incredibly strong she has been this week.
"As a proud Jawoyn woman she was particularly looking forward to wearing our Indigenous Round jumper in Launceston this weekend.
"We have a very close group of players and staff, and all our thoughts will be with her as we run out against the Bulldogs on Saturday."
King played in North Melbourne's breakthrough 2024 AFLW premiership, but was a hard-luck story last year.
She recovered from a knee injury to put her hand up for selection, but was deemed too big a risk for the grand final, watching from the sidelines as the Kangaroos went back-to-back.
Darren Crocker's team have made a strong start to their bid for a third consecutive flag, winning their opening two games of the new season.
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