Halfback Aaron Smith, flanker Shannon Frizell and prop Ethan de Groot won't join the Highlanders until mid-to-late January.
That has seen Otago players James Arscott and Sam Fischli step-up as cover at halfback and flanker, respectively, while Tasman prop Luca Inch has also been added.
Patelesio Tomkinson will miss the Super Rugby Pacific season due to surgery he required for an injury suffered to his left foot in the final of the Bunnings Championship against Taranaki last month. Taranaki wing Vereniki Tikoisolomone has been added to the squad.
Head coach Tony Brown said Tomkinson, who has played 31 games in the midfield and on the wing for the Highlanders, had suffered some hard luck.
"Sio has grown steadily as a player over the last few years and has always been a player we could rely on to perform consistently for us. He had another good season for Otago.
"It's a blow for us to lose him but a good chance for Vereniki to showcase his talent," he said.
Tikoisolomone scored five tries during Taranaki's unbeaten national provincial campaign in 2021. An elusive player with speed, he first revealed his try-scoring knack for Wanganui in the 2019 Heartland Championship, scoring 13 tries.
Flanker Billy Harmon also needed injury cover. He injured his shoulder during a Canterbury training session in October. He required surgery and is unavailable until early April. Christian Lio-Willie has been selected as cover for him.
New Zealand Under-20 halfback this year, Nathan Hastie, is covering for Folau Fakatava. Fakatava tore his ACL during the Highlanders' win over the Crusaders in Christchurch earlier in the year and is unlikely to complete his rehabilitation until the early rounds of Super Rugby.
Brown said the opportunity provided for replacement players was exciting.
"It is always interesting to see how replacement players respond to the opportunity to come into the squad. They're coming in off good provincial form and normally add extra enthusiasm and energy to our environment.
"It's a chance for them to stake a claim in the pre-season and demonstrate they belong at Super Rugby level," he said.