The Kiwis are wary of an unbeaten Fiji who top Pool D after downing Italy 38-10 on Friday, but Johnson said it would be a huge disappointment if New Zealand failed to go on to book a spot in the tournament decider.
"I haven't thought that far ahead. With what I believe we can achieve, yes (it would be a failure), but we can't look past next weekend.
"We've got to take a different road now but we're up for it."
Coach David Kidwell said defence and discipline needed to improve to limit the chances given to the likes of Fijian five-eighth Jarryd Hayne, fullback Kevin Naiqama and wing Suliasi Vunivalu.
"They can score from anywhere and have a very strong back five, and they're in form, we have to make sure we're on our defensive game," Kidwell said.
"There are some areas we need to improve on and (the players) were honest about those areas in the sheds and with the little things that make up the big picture.
"Kick pressure at the right times, making sure we complete our sets and get to our kicks, so we can get back into the grind of the game."
Meanwhile, Kiwis centre Dean Whare has returned to Australia for his uncle's funeral and will rejoin the side in Wellington tomorrow, while wing Dallin Watene-Zelezniak is in doubt for the weekend with a knee injury.