The star No 8 has been ruled out of the remainder of the Super Rugby Pacific season.
Renton had been tentatively scheduled to make his return against the Force at the weekend after a layoff that began when he suffered a high ankle sprain in the gutsy win over the Waratahs in the third round.
But he was scratched from the bench for the Force game, and it has been determined he requires surgery that will end his campaign.
It is a rough blow for the Highlanders, who followed a five-game losing streak with a one-point win over the Force on Saturday in one of the ugliest games in Super Rugby history, and are still in the playoff hunt.
Renton was their best player in 2023 and had started this season well.
He offers a blend of physicality and explosiveness that nobody else in the squad can match.
Nikora Broughton has athleticism and Tom Sanders has size, but it seems the Highlanders might be going to stick with putting captain Billy Harmon, who is back to the blinding form that must have him in the All Blacks frame, at the back of the scrum.
The Highlanders have also revealed Jonah Lowe is gone for the season.
Lowe, seen as a valuable member of the squad as he has some experience and covers both wing and centre, came home from the recent trip to Australia with an ankle problem and it has been confirmed he requires ACL surgery.
It will likely mean he also plays no part in the NPC for Hawke’s Bay.
Highlanders first five Rhys Patchell has a pectoral muscle injury and is undergoing further assessment, while winger Jona Nareki is out another three to four weeks with a hamstring strain.
Green Island fullback Finn Hurley, who also covers first five, has been upgraded to a full squad member as cover.
The possible loss of the classy Patchell means the Highlanders will again ask youngsters Cameron Millar and Ajay Faleafaga to get to grips with this level of rugby.
"There have been patches that they’ve gone really well," assistant coach Tom Donnelly said yesterday.
"Obviously they’re still really young players, and they’re still learning the game.
"The best thing about having Rhys around is he’s been working hard with those guys around how they build their week and how they prepare for games."
Donnelly acknowledged the Highlanders had a "good, honest review" into the atrocious game against the Force that at least ended in a win for the home side.
"I suppose the pleasing thing for us is that we still managed to win the game, and if you look across the stats we measure, we did a lot better than we have the last few weeks.
"Our game is getting better. We’re still just making too many errors in crucial areas of the field.
"We’re a lot better side than that. We created a lot of opportunities, and little handling errors let us down, from trying too hard.
"Is it something we’re proud of? No, but we’re proud of the result. It puts us in a better spot."
He said the Highlanders would do some training with a wet ball this week to prepare for the expected hot and humid conditions in Tonga for their game against Moana Pasifika on Saturday afternoon.
"We’re also working on mental skills, and how to reset from errors.
"The reasonably young group we’ve got, we’re making errors and we’re not able to flush them quickly to get back into the game."
Heritage jersey
The Highlanders have released their heritage jersey.
It is inspired by the 1997-99 era in which the Highlanders bounced back from the wooden spoon to be semifinalists in 1998 and finalists in 1999.
The era featured the arrival of beloved coach Tony Gilbert and featured stars like Jeff Wilson, Taine Randell, Anton Oliver and Tony Brown.
The retro design features the familiar tartan pattern over the shoulder.
It will be worn by the Highlanders in games against Moana Pasifika on Saturday and the Crusaders a week later.
