McKenzie continues in the All Blacks starting line-up for an eighth successive game on Saturday against France in Paris but with words of warning ringing in his ears.
"He has to learn how to play test rugby and test rugby is not like Super Rugby where you can do audacious things and get away with them,” Hansen told a news conference on Thursday.
"We don't want to stop his flair, but he's got to get better at the risk and reward concept of what he's trying to do.
"I've said he's like a fly in a bottle and he's getting better at that. He's still learning, but he is an exciting prospect," added the All Blacks coach.
Hansen said McKenzie was now challenging Jordie Barrett, out of action after shoulder surgery, for the back-up fullback role behind Ben Smith.
The 31-year-old Smith has taken a six-month sabbatical from the game and not played since August when he was on the wing against Australia in the Rugby Championship clash in Dunedin while McKenzie played at fullback.
But McKenzie offers other options and Hansen said he would play flyhalf in Super Rugby for the Chiefs next year.
“Deep down in my heart of hearts I think that's where he'll end up playing most of his rugby."
McKenzie said defeat in the All Blacks’ last match against the Wallabies in Brisbane last month had been “a good learning".
"Just around my option-taking, what's right and not right, and being smart around my footy. At times I like to take a few risks, but it's trying to get that balance between high risk and high reward," he said.
"It's not about changing anything dramatically, but improving the little things, the most important things. I learnt a lot that game.
“Coming off a loss you want to get straight back out there and prove yourself again. It's been a long three-week wait. It was my first loss in the black jersey and took a while to sink in,” McKenzie said.
(Writing by Mark Gleeson,; Editing by Ed Osmond)
