The key forward's inability to recover from his pre-season injury has been a disaster for the Saints, who are in the bottom four after Saturday night's fighting loss to Collingwood.
Also on Monday, reports said Saints young gun Mattaes Phillipou would be out for several weeks. He was distraught after aggravating a lower-leg injury only minutes before of the start of the Collingwood game and was a late withdrawal.
King has not played since round 17 last year, but the Saints had been hopeful he would return before the end of this season.
He has already needed two operations on his right knee because of the initial injury during a February practice match.
The Saints re-signed King to a six-year deal last season, taking him to 2032.
In a statement, the club said Monday's surgery was on damage to the medial aspect of the knee, which had caused "occasional but persistent" pain.
The Saints are also adamant they have been baffled by King's ongoing problems.
"Max's case has not been simple nor linear, and we've attempted to adequately keep our members and fans up to date while maintaining Max's privacy," said Saints football boss Dave Misson.
"We have also been dealing with a medical situation that has often confounded the many medical experts we have consulted."About 10 days ago, as Max was closing in on a return to football, he felt a clunking in his knee - the same knee that has been causing him trouble throughout this season."This was as surprising as it was frustrating, as all indications were that Max's most recent arthroscope had addressed this issue."
That meant more consultations and scans, leading to Monday's surgery.
"We feel the cause of Max's issue has been pinpointed and that damage to the medial aspect of his knee, in certain situations, was impeding his movement and causing pain," Misson said.
"The operation aimed to address and repair this issue. It will see Max off-legs for several months, however, will allow him to be ready for the commencement of pre-season."
Meanwhile, the AFL website reported Phillipou would be out for several weeks after his plantaris tendon injury flared again before Saturday night's match.
Phillipou was a late scratching when he felt sharp pain in his calf while warming up.
Injuries have restricted him to only four games this season.
14°C