St Kilda defender Jimmy Webster has been given a seven-match suspension for rough conduct against Jy Simpkin after pleading guilty to the serious charge.

Webster's ban was the longest suspension the AFL tribunal has delivered in six years.

The tribunal on Tuesday evening found that Webster acted with an intention to bump "at the highest end of careless", the act was "entirely avoidable", and Simpkin was vulnerable and not in a position to protect himself.

The result of Webster's actions left Simpkin with a third concussion within the past 12 months and, as of hours before the tribunal hearing, North Melbourne confirmed the Yorta Yorta star will miss its opening clash of the 2024 season against GWS Giants.

Webster's return could be against North Melbourne should St Kilda coach Ross Lyon not send him back to the VFL.

The landmark case for the AFL has set a new precedent in the game's bid to protect its players from concussion while Webster threw himself at the mercy of the tribunal by pleading guilty.

Webster had been referred straight to the tribunal to plead guilty after his high bump contacted the head of one of the Kangaroos co-captains in the first quarter of Sunday's practice match.

Webster left the ground as he bumped Simpkin, catching the North midfielder both late and high.

The match review officer (MRO) graded the act as rough conduct that was careless, high contact and severe impact.

The AFL had asked for an eight-match ban, taking into account Webster did not make an argument against the allegations and he had shown remorse.

St Kilda argued that the eight-match ban would be a "excessive and disproportionate" sanction given the "unintentional and careless nature of the action", according to club advocate Adrian Anderson, the AFL's former football operations boss.

"What is proposed is a massive, sudden shift in sanction that is out of whack with the evolution over time," Anderson said.

Anderson, in Webster's defence, cited Andrew Gaff's eight-match ban playing for West Coast after famously striking Fremantle midfielder Andrew Brayshaw in 2018, which he added was a "deliberate act that smashed his opponent's jaw".

Webster is the second man to be banned before the season's start after Ballardong and Whadjuk Noongar onballer Sam Powell-Pepper copped a four-match suspension for rough conduct after his high but less severe bump concussed Adelaide defender Mark Keane when Port met the Crows.

Anderson also argued Webster's bump was comparable to the Powell-Pepper incident and a similar length ban would be an appropriate sanction.

Despite the one suspension in his decade-long career and having references from St Kilda board member Jack Rush, a high-profile lawyer, and former Saints coach Alan Richardson, Webster copped twice the penalty received by Powell-Pepper.

St Kilda confirmed at the end of the hearing that the club would accept the sanction and would not challenge via an appeal.

"I'm really sorry about what happened on Sunday," Webster said exiting the tribunal.

"It's something I'm not proud of (and) I've let a lot of people down.

"I don't really have an excuse as to why. It's such a quick decision and clearly I got it wrong."

Webster was not taking his actions or the verdict lightly, and reflected on Simpkin's well-being in the 48 hours between the end of the practice match and facing the tribunal.

"I understand how bad concussions are and how much we want to see them stamped out," he said.