Webster was sent straight to the tribunal over the high, late hit that left North Melbourne co-captain Simpkin in concussion protocols, and the Saints have already conceded they won't defend it.
The 30-year-old will face the tribunal from 5pm (AEDT) on Tuesday.
Saints coach Ross Lyon said on Monday there was "no defence" for Webster's actions, while football boss David Misson labelled the incident "out of character".
Webster has also issued a statement, wishing Simpkin well in his recovery.
"I deeply regret my actions in (Sunday's) game," Webster said.
"I've reached out to Jy and cannot understate (sic) my remorse."
The action was graded by the match review officer as careless conduct, severe impact and high contact.
Jy Simpkin (left) had to spend the rest of Sunday's match on the bench after being bumped. (Joel Carrett/AAP PHOTOS)
Given the AFL's focus on protecting the head, Webster appears poised to cop a lengthy ban of at least six weeks.
"As I looked at it - and St Kilda have been already on the record today as saying that - this is an action that we don't need in our game and we don't want it in our game," chief executive Andrew Dillon told Fox Sports' AFL 360.
"So it was really clear to me it was going to be going straight to the tribunal, and the MRO looked at it today and that's where they've sent it."
The incident happened four days after Port Adelaide forward Sam Powell-Pepper received a four-game suspension for a bump that concussed Adelaide defender Mark Keane.
"If you look at the Webster one compared to Powell-Pepper, there are differences, and I think they would be taken into account when we come to a sanction," Dillon said.
"I'm probably not going to put a number (of weeks) on it now but ... the community expectations are changing, and the AFL - we have to be at the forefront of that and we have to evolve with the community standards changing."
Gold Coast coach Damien Hardwick and Carlton counterpart Michael Voss were both taken aback by the incident and intrigued to see what suspension Webster would face.
"Look, it'll be a pretty significant penalty," Hardwick said.
"We understand where we're at in the game at the moment with the concussion protocols and the concussion history going through the game at present.
"So it'll be a rather lofty suspension I would say."
Voss noted: "I think all parties have stepped back and accepted that it's probably not what we want in the game."
The incident prompted a fiery exchange between Kangaroos coach Alastair Clarkson and Webster and teammate Dougal Howard.
Clarkson has been issued a "please explain'' from the AFL over the confrontation, which included the alleged use of a homophobic slur towards the St Kilda players, and could face his own sanction.
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