Withy has been suspended for three weeks following his upgraded red card during the Super Rugby Pacific game against the Force in Perth on Saturday night.
The No 8 slid in to attempt to prevent Force winger Harry Potter scoring a try in the 48th minute but ended up collecting Potter in the head with his knee.
The Super Rugby Pacific Foul Play Review Committee found Withy guilty of reckless or dangerous play.
A mid-range entry point of six weeks was appropriate for the incident, the committee determined.
But as Withy accepted his guilt, and his previous disciplinary record was sound, he received the full 50% reduction in sanction.
Withy was also given permission to attend World Rugby’s coaching intervention programme to cut the ban to two weeks.
He will miss Saturday night’s game against the Fijian Drua and the game against the Chiefs in Hamilton a week later.
Withy has been an ever-present for the Highlanders in recent times, regularly leading the tackle count, and has held the fort at No 8 over the past two weeks despite being a natural flanker.
The Highlanders should at least have the likes of Hugh Renton, Nikora Broughton and Oliver Haig returning soon from injury to alleviate his absence.
