King hurt his left shoulder in the opening seconds of the Saints' 21-point loss to Melbourne on Saturday night and was substituted out of the game.
It is the same shoulder King had reconstructed in December after a fall at training.
Saints coach Ross Lyon, who suspected post-match King's latest setback was "significant", confirmed the club's worst fears on Sunday.
"We just had a meeting this morning on it. He'll go and see the surgeon tomorrow ... he's done for the year," Lyon told 3AW.
"It was a dislocation out the front, so it's heartbreaking for him and us, but he will return."
King missed the opening nine rounds of the season but marked his comeback with four goals in round 10.
The 23-year-old - the Saints' leading goalkicker in 2021-22 - booted 14 majors in six appearances this season before re-injuring the shoulder.
Lyon said King's family and management will be part of the process to determine the best course of action from here as the Saints map out another rehabilitation program.
"You've got to fill them with air and belief and make sure that we're doing the right thing, so we feel we can do that," Lyon said.
"I feel for the King family and none more than the boy himself."
St Kilda also lost Seb Ross (hamstring) and Zaine Cordy (concussion) before quarter-time against Melbourne.
They fought bravely but were ultimately overrun in a loss that puts their top-eight spot in jeopardy.
The Saints (9-7) won their first four games of the year in Lyon's second coming as coach but have now lost four of their last six matches.
They face a difficult road trip to take on fellow finals hopefuls Gold Coast in round 18.
11°C