Frizell joins injured list as All Blacks depart for Rugby World Cup
Speaking to reporters at Auckland airport before flying to Europe, Foster said Frizell had tweaked a hamstring during training.
The flanker is on a "similar time frame" to lock Brodie Retallick, who is expected to miss the All Blacks' next two games with a knee injury, Foster said.
New Zealand play a final tune-up game against South Africa in London next Friday, then face hosts France in the World Cup's opening game on September 8th.
Foster said the dual injuries "are a bit niggly for us" but is confident in the cover for Frizell and Retallick against South Africa.
"We'll have to re-assess and see what happens after that Test."
The All Blacks boss said they had learnt from the fall-out surrounding Owen Farrell's red card.
The England fly-half could miss the start of the World Cup after governing body World Rugby announced it would appeal the controversial decision to overturn Farrell's red card for a high tackle in a warm-up win over Wales.
"The whole alignment between refereeing and judiciary is something we are all conscious of going into a World Cup," said Foster.
"The only way we can control that process is by making sure we get our techniques right.
"You never want to leave your destiny in the hands of the judiciary."
New Zealand head to France bidding to win the World Cup for a fourth time, having won all four games so far this year including a 35-20 home win over reigning world champions South Africa last month.
Foster said he would play his strongest available team in the warm-up against the Springboks.
"I won't be protecting anyone. You don't win World Cups by putting people in cotton wool," he added.
After four years in charge, Foster will stand down following the World Cup to be replaced as All Blacks boss by ex-Canterbury Crusaders coach Scott Robertson.
Foster said he had put last year's poor results behind him.
The All Blacks lost four times in 2022 including two home defeats to Ireland and a first loss to Argentina on New Zealand soil.
"Will I reflect on that? No I won't - there is too much to do now," said Foster.
"We have a great occasion in front of us.
"The key with World Cups is you don't want to waste a day."
