The Highlanders captain was – literally – axed from the derby against the Crusaders at Forsyth Barr Stadium on Saturday evening.
“Billy got a cut on his hand just before half-time in Tonga, so it had to be stitched up,” Highlanders coach Clarke Dermody said today.
''Unfortunately it is not cured. He's simply not in a position to play this week, but we hope this won't keep him out for too long.”
Nikora Broughton will replace Harmon at No. 8, while the captaincy will fall to Ethan de Groot, who was rested when the Highlanders played Moana Pasifika in Nuku'alofa but will regain the No. 1 jersey for the Crusaders.
It will always be the plan for De Groot, who made the most of his time at home in Southland for the duck shooting weekend, to miss the Tongan trip to count as an All Blacks rest week and prepare for the old enemy, said Dermody.
''He had a great weekend. He was still training hard. He was back in good form before he left, so he's really motivated against a pretty powerful scrum.”
There is also a change at the other end of the scrum, where Jermaine Ainsley will look to turn his injury-hit season into a fond farewell as he counts down the weeks until he heads to France.
The only other change to the starting XV is on the left wing, with Martin Bogado replacing Connor Garden-Bachop, who was having an excellent game in Tonga before suffering a head knock.
Young midfielder Jake Te Hiwi retains the number 12 shirt for the third week in a row.
It is a reasonable point for discussion, because it means that vice-captain Sam Gilbert will remain on the bench again.
“Jake is playing well,” Dermody said. ''As always: if you play well, you will be selected.
''We felt that Sam's form had not dipped but had stagnated a bit mid-season, so Jake got his chance and he is playing well.
''Sam still plays a big role in the team. He is one of our senior leaders and he has a big job to do.”
Otago youngsters Will Stodart and Finn Hurley will be in the reserves.
The Highlanders are feeling uplifted after back-to-back wins and knowing 15,000 tickets have already been sold for the game.
While the Crusaders are struggling – and in fact having a terrible season by their ridiculously high standards – Dermody wouldn't be swayed if it was suggested they could be there for the taking.
''I think every time we play the Crusaders is a great occasion.
''We haven't played them at home for a few years and the rivalry has been there since day one of the competition, so the boys are really looking forward to it.
''There is always an increase in intensity for natural reasons. You know, we're neighbors. The boys are very enthusiastic.
''I think they are a quality team. They have good players on the pitch, so we prepare for their best and we know we have to play well to beat them.
“It's another opportunity for us to play the Crusaders, which is the highlight for us here.”
Highlanders team to play Crusaders
Jacob Ratumaitavuki-Kneepkens, Timoci Tavatavanawai, Tanielu Tele'a, Jake Te Hiwi, Martin Bogado, Cameron Millar, Folau Fakatava, Nikora Broughton, Sean Withy, Oliver Haig, Fabian Holland, Mitch Dunshea, Jermaine Ainsley, Henry Bell, Ethan de Groot (captain).
Reserves: Jack Taylor, Ayden Johnstone, Saula Ma'u, Will Tucker, Will Stodart, James Arscott, Sam Gilbert, Finn Hurley.