The 23-year-old, who endured fierce criticism for his performance in a close defeat to Port Adelaide on Sunday, hurt his posterior cruciate ligament just after halftime against the Power.
The injury is on the same left knee that led to King missing two matches earlier in the season. St Kilda believe the injuries are unrelated.
Max King had kicked 19 goals from 12 games for St Kilda this season. (Julian Smith/AAP PHOTOS)
"This is a very disappointing outcome for Max," Saints football boss David Misson said.
"It's a credit to Max's commitment to his teammates that he played out the game on Sunday, but for his long-term future and health, it's important we now give his knee some time to rest and recover.
"While this will see Max miss the rest of the season, pleasingly he doesn't require surgery, and this course of action will place him in the best possible position to attack pre-season."
King had kicked 19 goals from 12 games this season, but his performance against Port came under fire before his latest injury was revealed.
St Kilda made the finals last year, with King playing a crucial role in the Saints' charge once he was available mid-season following shoulder surgery.
St Kilda head coach Ross Lyon praised Max King's mental strength after the Port defeat. (Joel Carrett/AAP PHOTOS)
Saints coach Ross Lyon defended King on Sunday after he went goalless against Port.
"When we're not getting a lot of clean ball to him, it can be hard … I really admired his mental (toughness) ... he took a step forward," Lyon said.
The Saints have slumped to 15th on the ladder with a 5-10 record.
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