Northampton flanker Calum Clark has been suspended for 32 weeks following an incident in which Leicester's Rob Hawkins suffered a broken elbow.
The 22-year-old was cited during Northampton's LV= Cup final defeat against Leicester on 18 March, and then banned indefinitely by his club.
Clark pleaded guilty to a charge of hyperextending Hawkins' right arm at a Rugby Football Union hearing.
Hooker Hawkins, 28, could be out for three months.
No card was issued following the incident
during the match at Worcester, which Leicester won 26-14.
Calum Clark factfile
- Age: 22
- Position: Flanker
- Club: Northampton Saints
- Capped by England at U16 and U18 level
- Part of England U20 side defeated 38-3 by New Zealand at Junior World Championship final in 2008
- Joined Northampton from Leeds in 2010
- Voted the Saints' Young Player of the Season for the 2010-11 campaign
- Selected as part of the 2012 England Elite squad
Tigers' head coach Richard Cockerill afterwards described Clark's actions as "completely out of order".
He told BBC Radio Leicester: "If Calum Clark is deemed to have done it on purpose it's pretty horrendous.
"It's a pretty poor act. I think it's completely out of order and, in my opinion, it's as bad an injury as I've seen on a rugby field."
Clark was cited by the RFU the following Wednesday and faced a charge of an act contrary to good sportsmanship when he appeared before the panel chaired by His Honour Judge Jeff Blackett.
The ban is dated from 22 March-1 November and the forward will also pay hearing costs of £500.
A Northampton statement said: "The disciplinary panel found that Calum Clark had not intended to injure Rob Hawkins in the course of moving his arm. Accordingly the unfortunate injury suffered by Rob Hawkins was unintentional.
"In the light of that finding of the disciplinary panel, Northampton Saints is bound to express concern and disappointment at the imposition of such a long suspension, even after significant mitigation in recognition in what was accepted to be Calum Clark's genuine remorse.
"Accordingly the club is bound to consider the merits of an appeal."
Clark joined Saints from Leeds Carnegie in the summer of 2010 and last September agreed a new three-year contract with the club.
He was named in Stuart Lancaster's new-look England elite player squad for the recent Six Nations but has yet to make his first senior international appearance.
Clark is not the only Saints player who will miss the Premiership run-in as England hooker
Dylan Hartley received an eight-week ban on Tuesday for biting Ireland flanker Stephen Ferris
in the Six Nations international at Twickenham on 17 March.