And though judicial officer Terry Willis opted against handing down the maximum 18-week punishment, the suspension will end Leslie’s World Cup campaign.

The verdict could also mark the end of the 32-year-old’s international career but was inevitable after the three-man Rugby World Cup disciplinary panel saw television replays of the incident.

Leslie pleaded not guilty to the offence, but the playbacks clearly show him pulling Keyter over the top of a ruck, then driving his right knee into the side of his opponent’s head.

The player left the hearing without comment, while Scotland team manager Dougie Morgan said a statement on the outcome would be released once the Scots had digested the full implications.

“We have not yet decided whether to appeal,” confirmed Morgan.

In his 37-cap international career, Leslie, brother of former Scotland captain John, had never been sent off or cited.

However, Willis said the TV evidence left him with little option other than to deliver a hefty punishment, the biggest ever handed out to a Scottish international for an incident occurring in a Test match.

“The clearest angle of the incident shows that Leslie, of his own volition, pulled the jersey of Keyter, dragging him onto the Scottish side of the ruck,” said Willis in a statement.

“He had ample space after dragging the American player down to avoid contact between his right knee and the head of the player.

“I reject the argument that he used his right leg to propel himself forward and find that he deliberately dropped his knee into the head of the player.

“I am mindful that a significant period of suspension is required to mark my concern over the unnecessary and dangerous use of the knee by Leslie on the head of the American player who was in an unprotected and vulnerable position.”