Loose forward Ethan Blackadder has been called into the New Zealand squad for the Rugby World Cup as an injury replacement for winger Emoni Narawa, coach Ian Foster said on Saturday.

Narawa was ruled out of the tournament with a back injury earlier in the week, but Foster said Blackadder's inclusion was as much a reaction to captain Sam Cane being a late injury withdrawal from Friday's opening loss to France.

"Ethan should be here Monday afternoon and that's a replacement for Emoni," said Foster. "I guess with Sam Cane and his back popping out the last couple of days means we're just going to reinforce the loose forwards stock."

Cane joined flanker Shannon Frizell, prop Tyrell Lomax and centre Jordie Barrett in the treatment room but Foster did not rule out his skipper playing a part in the second Pool A match against Namibia next Friday.

"We're just doing our medical stuff now but he's certainly better than what he was yesterday, which was great, and then he was better yesterday than he was on Friday," Foster said.

"I don't anticipate this being a long-term thing. Whether it's right for Namibia or not, I couldn't tell you at the moment, but the medical staff don't seem to be concerned by it at the moment."

Foster said Frizell, who has a hamstring problem, would definitely not be fit to face Namibia and Lomax was unlikely to have recovered from a cut that caused muscle damage to his leg that he sustained in a warm-up loss to South Africa.

There was a better prognosis for Jordie Barrett's sore knee, he said.

"Jordie is getting better every single day. So we'll just make that decision as we go along," Foster added.

"There's going to be a little bit of an ongoing management with him so it's just going to be a matter of his progress the next two days."

One positive from Friday's defeat was lock Brodie Retallick, returning ahead of schedule from a knee injury, moving onto the bench in the rejig after Cane's withdrawal and coming on as a second-half replacement.

"We've got a few tight calves and a few sore bodies, but I think we come through that really well," said Foster.

"And that injured group is progressing really strongly. Brodie was a great example. He went on for his 15 minutes and came through really well."