"Our thoughts are with Jimmy, he has been an outstanding leader for us over the preseason and the early rounds of the competition," Highlanders head coach Aaron Mauger said in a statement.
"The whole squad join with me in wishing the skip a successful recovery and we look forward to seeing him around the environment post-surgery."
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The Highlanders have named Otago loose forward Slade McDowall as Lentjes' injury replacement, while the squad's two vice-captains – Aaron Smith and Ash Dixon – will fill the captaincy void as co-captains.
A Super Rugby call-up is good reward for 21-year-old McDowall, who has impressed for Otago since making his Mitre 10 Cup debut three years ago and was unlucky not to have received a full contract with any franchise this season.
The Otago Boys' High School product trained with the Highlanders on an interim training contract over the pre-season, and Mauger revealed that he came very close to earning selection in the full squad.
"Saw his performance in the Mitre 10 Cup, thought he was outstanding, saw a lot of growth in his game, so he's another guy we've tracked really closely and he's not too far off," Mauger told RugbyPass in November.
"Really excited about having him through the pre-season to keep developing his game and learn a bit more about him."
McDowall joins his former New Zealand Schools teammate, ex-New Zealand U20 star and Canterbury lock Will Tucker as two new additions to a 27-man travelling squad which has departed for a two-match tour of South Africa and Argentina.
Tucker's addition to the Highlanders bolsters the side's stocks at lock, as the likes of Pari Pari Parkinson and Josh Dickson have been left at home to mend some minor injuries that prevented them from facing the Rebels over the weekend.
The defeat to the visiting Australian outfit leaves the Highlanders clamped to the bottom of the New Zealand conference with just one win from four matches, while they sit in 13th place on the overall standings.
The flailing Dunedin franchise will look to overturn their fortunes when they take on the Bulls in Pretoria this weekend before going on to play the Jaguares in Buenos Aires a week later.
Highlanders touring squad to South Africa and Argentina
Backs: Aaron Smith, Kayne Hammington, Mitch Hunt, Josh Ioane, Teihorangi Walden, Ngane Punivai, Jona Nareki, Michael Collins, Tima Fainga'anuku, Scott Gregory, Josh McKay.
Forwards: Ayden Johnstone, Liam Coltman, Ash Dixon, Nathan Vella, Jeff Thwaites, Siate Tokolahi, Daniel Lienert-Brown, Manaaki Selby-Rickit, Jack Whetton, Will Tucker*, Slade McDowall*, Dillon Hunt, Shannon Frizell, Marino Mikaele Tu'u, Jesse Parete, Teariki Ben-Nicholas.
This article first appeared on RugbyPass.com and has been republished with permission