King has one final hurdle - a team training session on Friday - but has otherwise been cleared to face North Melbourne at Marvel Stadium on Sunday.
The 26-year-old underwent knee surgery and most recently battled a hamstring injury, with St Kilda coach Ross Lyon declaring he was good to go for the crunch match.
"As long he gets through training, he's done an enormous amount of work," Lyon said on Thursday.
"Certainly back to '23 volumes and running numbers and he looks strong and fit, so we expect him to get through tomorrow and play.
"He's done so much more work than ever in his last VFL return, bigger sessions, in percentage terms, you're talking 30 or 40 per cent more and we overlaid it with his '23 return when he went straight into the Giants and when we kicked two lazy goals in the first quarter.
"It's not going to be easy, we get that, but he's just in such better physical and mental shape."
Standing 202cm, King will bring some much-needed height to the Saints.
Lyon said ruck Tom De Koning, who is still recovering from a rib injury, was "unlikely" to be named.
The veteran coach stated his side was the smallest line-up, on average height in the competition last round, when they were well-beaten by Geelong.
"He's going to help, he's a big man, " Lyon said of King.
"We were the most intercepted team against in the air over the last four or five weeks and it's been a challenge so that will help."
King kicked 28 goals in 11 games in 2023 then 19 goals in 12 games in 2024, but was injured in round 17 that season.
Lyon tried to temper expectations of a 2023 output by King in his first match, but hoped he would build on that.
Sitting 10th with an 8-10 record, victory is crucial against the Kangaroos who are 13th but on the same competition points and hunting a wildcard playoff berth.
"It's an expectation going forward that there's an excitement that we know he's a quality player," Lyon said.
"Off all his analytics, he's just a high-end forward ... but at the minute, it's just one step of a bigger picture really. But it's a really exciting one for all our Saints fans."
