New Zealand's back-row options were depleted on Monday after confirmation Matt Todd broke his hand during Canterbury's Mitre 10 Cup clash with Otago.
Todd has only been a bit-part player for Steve Hansen's side but made five of his eight All Blacks appearances last year.
He was expected to be in contention for New Zealand's next Rugby Championship match against Argentina on September 9 after Sam Cane failed a head injury assessment last weekend.
Cane and centre Ryan Crotty were not cleared return to Saturday's last-gasp 35-29 win over Australia in Dunedin, and both are doubts to face the Pumas.
Were Cane to miss out Todd would be in the frame - along with Ardie Savea - to come into the pack, but the 29-year-old is set for time on the sidelines himself.
"Matt Todd fractured his left hand and will be in a splint for four weeks," Canterbury posted on their Facebook page.
"A hand specialist and team medical staff will continue to monitor his recovery and after this time he will be reviewed by the specialist before being cleared to play."