Telea was the first choice left winger coming into the tournament and scored two tries in the opening loss to France and another in the 96-17 thrashing of Italy.
"It was a breach of protocol," said Foster on Thursday. "Nothing major, but enough to keep him out of selection for this week. We still love him and he's training well so let's see what happens.
"It is what it is," he added. "Just for us, it's pretty clean cut, I don't really want to talk about it anymore. We've dealt with it as a team and moved on.
"We believe in what we stand for. And I think that it speaks volumes for the team that we're willing to make that sort of decision in this sort of week."
Foster gave Fainga'anuku a runout in New Zealand's last pool game against Uruguay and the power winger responded with a hat-trick. He showed his versatility by finishing the game in the centres.
Foster said the All Blacks were fully prepared to take on the number one team in the world on Saturday and said the loss to the Irish in a home Test series last year would mean nothing.
"This team is ready," he said. "If you look at this year, the whole thing is about getting ready for a World Cup and making sure we're primed to perform at this stage of the tournament.
"We're excited by the challenge, we know how good Ireland are, and they deserve all the plaudits they get, but play-off rugby is about who's best on the day."
Other than Telea's omission, there were no big surprises in the team.
Foster brought back all of his big guns, with No.8 Ardie Savea, fullback Beauden Barrett, lock Scott Barrett and scrumhalf Aaron Smith all returning to the starting line-up after being rested against Uruguay.
In the front row, loosehead prop Ethan de Groot returns after suspension and Tyrel Lomax starts at tighthead having recovered from a knee injury.
In one minor surprise on the bench, Finlay Christie was preferred to Cam Roigard as back-up to Smith at scrumhalf.
New Zealand team: 15-Beauden Barrett, 14-Will Jordan, 13-Rieko Ioane, 12-Jordie Barrett, 11-Leicester Fainga'anuku, 10-Richie Mo'unga, 9-Aaron Smith, 8-Ardie Savea, 7-Sam Cane, 6-Shannon Frizell, 5-Scott Barrett, 4-Brodie Retallick, 3-Tyrel Lomax, 2-Codie Taylor, 1-Ethan de Groot.Replacements: 16-Dane Coles, 17-Tamaiti Williams, 18-Fletcher Newell, 19-Samuel Whitelock, 20-Dalton Papali'i, 21-Finlay Christie, 22-Damian McKenzie, 23-Anton Lienert-Brown.
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