As Nasiah Wanganeen-Milera dragged the Saints to a vital 31-point win with another Marvel Stadium masterclass, the club's golden hope up forward was unable to finish the match.
King left the field in the third quarter of St Kilda's 13.15 (93) to 8.14 (62) win due to hamstring tightness.
The 26-year-old will undergo scans, but wasn't spotted again - even in the team song - after being taken to the rooms.
King earned just two possessions, including missing a difficult shot on goal in the second term.
It was King's first AFL game since June 30, 2024, having battled knee injuries as well as soft-tissue concerns.
He had two games at VFL level earlier in the year but suffered a hamstring injury in one of those, pushing back his comeback past the two-year mark.
Lyon declared King had trained strongly in a four-week block to justify playing him on limited minutes against the Kangaroos.
"I don't even know what the outcome is, so how can it be an error before there's an outcome," Lyon responded to repeated questions about King.
"But we stand by our decision to play (him). We have high-performance experts ... we have conditioning, we're really quite confident.
"Hindsight's 20-20, isn't it?
"You can't be timid souls sitting in the sidelines.Â
"We're in the arena making decisions."
Lyon laughed when asked for further detail on King's injury and his welfare, saying he had already answered it.
"It's about resilience and coming again," Lyon said.
"He's run down an AFL race, feels good, had a start, get a feel for how hard it is, and rehab a potential soft tissue injury.
"I haven't seen Max King, I was coaching, he wasn't in the rooms, he wasn't in the song.
"When we get the results, we'll update it. There's no angst.
"We've got to stand by the decision because we made it."
St Kilda (9-10) finish the round placed 10th, in a wildcard spot ahead of the final month of the season.
After starting strongly with a 16-point lead at quarter-time, St Kilda were fortunate not to be further behind than a goal during the third term.
The Kangaroos butchered numerous gettable chances all day, with Wanganeen-Milera's switch to deep forward reaping rewards for the Saints.
Nearly a year to the day since he inspired St Kilda to a famous comeback against Melbourne, Wanganeen-Milera produced a third quarter for the ages when he kicked three goals from 10 touches.
He inexplicably didn't poll three votes for his performance against the Demons last year, but the 23-year-old will surely have to earn the maximum this time for his four-goal, 46-possession domination of the Kangaroos.
Wanganeen-Milera also registered 1062 metres gained - more than half a kilometre greater than the game's next best, Saints' Darcy Wilson (489).
St Kilda were rocked by two late changes, pulling out Cooper Sharman (managed) an hour before the start, while ruckman Rowan Marshall suffered back spasms in the warm-up.
After a season of steady improvement, the Kangaroos' campaign appears shot as they sit a game and significant percentage outside the top-10.
Veteran Jack Darling capitalised up forward with three goals, but captain Nick Larkey continues to suffer the yips.
Once arguably the safest set shot in the AFL, Larkey has managed 6.15 in his past six games.
Charlie Comben was taken to hospital after a heavy collision late in the match, but Kangaroos coach Alastair Clarkson said doctors were confident the key defender hadn't suffered any internal damage.
"They're just taking him there for observation because he was just coughing up a little bit of blood," Clarkson said.
"It was a heavy hit, open to his chest area, but they seem to think he's going to be all right."
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