Senz reported the Highlanders captain announced this week he will not be returning to the club as he takes up a new opportunity overseas.
Harmon joined the Highlanders in 2021, after three season with the Crusaders, and took over the captaincy last season, which he retained this year.
He had also played for the Maori All Blacks since 2018 and was part of the All Blacks XV who played in Japan last year.
Harmon will co-captain the Highlanders alongside Ethan de Groot for their final Super Rugby Pacific round robin clash against the Hurricanes tomorrow.
The Highlanders, who currently sit sixth on the ladder, have taken the chance to rest some players after already having booked themselves a playoff spot.