Melbourne forward Danny Williams has copped the longest suspension in the seven-year history of the NRL judiciary, an 18-match ban for king-hitting Wests Tigers back rower Mark O'Neill.

It was the biggest ban for an on-field offence in 17 years of premiership football and threatened to end the 30-year-old's NRL career.

Williams' landmark "post traumatic amnesia" defence fell on deaf ears at a marathon four-hour hearing at league headquarters, the three-man panel sending him on the longest suspension since the NRL's 1998 inception and the longest since the Dragons' Steve Linnane copped 20 weeks for gouging Penrith's Greg Alexander in 1987.

Asked if he would appeal the hefty ban, Williams said: "We will be considering our options".

"I'm obviously disappointed with the outcome. I haven't really thought about it."

If Williams fails to successfully appeal the ban, the forward's NRL career is effectively over.

Williams is off contract at the end of the season with little interest from other NRL clubs and his ban carries over to the English Super League, limiting his chances of being signed by a rich UK club.

Williams was sent off for striking O'Neill in round 19 and has since served two matches of his ban while further medical evidence was gathered.

Dr Nathan Gibbs said at the initial hearing that Williams may have been concussed and suffering from post traumatic amnesia from a high tackle inflicted by O'Neill.

When the hearing resumed, judiciary chairman Greg Woods QC and panel members Darrell Williams, Ian Roberts and Bob Lindner were bombarded by medical evidence.

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