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.
Saints coach Ross Lyon defended King on Sunday after he went goalless against Port.
St Kilda head coach Ross Lyon praised Max King's mental strength after the Port defeat. (Joel Carrett/AAP PHOTOS)
"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.
King has kicked 159 goals across his 83-game career but has managed just 23 matches in the past two seasons after firing in 2022 with 52 majors.
Since being drafted in 2018, King has struggled with shoulder injuries, and was not able to debut until 2020 after missing the 2019 season due to an anterior cruciate ligament rupture.
St Kilda are ranked 15th in attack this season, just in front of bottom-placed North Melbourne.
The Saints have been highly reliant on their small forwards to kick goals, with King struggling and Tim Membrey playing in the VFL.
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