The Eagles led by 11 points early in the last quarter of Saturday's match, but three final-term goals to Mason Wood helped lift St Kilda to the 12.10 (82) to 10.8 (68) victory.
Reid faces a nervous wait after slinging Saints youngster Darcy Wilson to the ground in the third quarter.
The force and slinging nature of the tackle resulted in the back of Wilson's head hitting the turf.
Darcy Wilson received a free kick following this Harley Reid tackle.— AFL (@AFL) #AFLEaglesSaints pic.twitter.com/Rhs2htAPrsJune 1, 2024
Wilson went off to be assessed for concussion, but was later cleared to return.
If Reid is suspended, the prized No.1 draft pick will be ineligible to win the Rising Star award.
With raging hot favourite Reid in danger of being suspended and Western Bulldogs forward Sam Darcy now ineligible after copping a two-match ban, the award could be thrown wide open.
West Coast coach Adam Simpson said he didn't want to discuss the Reid tackle in too much detail for fear of getting into trouble with the AFL, but he's hopeful of a positive outcome.
"I thought there's nothing in it, that's what I'll say," Simpson said.
"I spoke to him and it was like, 'mate, I didn't think there was much in it, so keep going, keep working through the tag'.
"That stuff will work itself out. Whatever happens there, we'll deal with it."
Reid looked set to be the difference in Saturday's match after a 17-disposal, seven-clearance first half, but he was restricted to just three possessions in the second half after being tightly tagged by Marcus Windhager.
St Kilda's win came at a cost, with star forward Max King subbed off at three-quarter-time with a knee injury.
Saints coach Ross Lyon didn't attend the post-match press conference due to illness.
West Coast's Liam Ryan applied plenty of scoreboard pressure to the Saints, kicking three goals. (David Woodley/AAP PHOTOS)
Assistant Corey Enright is confident King's injury isn't serious.
"It's a jarred knee," Enright said.
"It's early. We had to sub someone out and he was under a little bit of a cloud, so it was an easy option for us.
"What it looks like going forward - we'll go back to Melbourne and scan and we're quite hopeful at this stage."
West Coast veteran Jamie Cripps and goalsneak Liam Ryan kicked three goals apiece, while Tom Barrass and Jeremy McGovern were exceptional in defence.
Wood finished with a game-high four goals to go with 22 disposals.
St Kilda's Mason Wood finished with a game-high four goals in the Saints' win over West Coast. (David Woodley/AAP PHOTOS)
West Coast suffered a huge late blow when Coleman Medal fancy Jake Waterman withdrew with a shoulder injury.
It came on the back of star midfielder Tim Kelly (hip) pulling out on Friday.
The opening term was an error-riddled affair, with St Kilda particularly guilty of butchering the ball in a quarter when their disposal efficiency was a woeful 52.1 per cent.
Reid amassed 13 disposals and six clearances during a monumental second-quarter display to help give West Coast a 14-point half-time lead.
Lyon sent Windhager to tag Reid in the third quarter, and the move worked a treat as the Saints took control of the match to secure their fourth win of the season.
