Smith,who is Highlanders captain and All Blacks vice-captain, was forced off the field late in the first half of Saturday night's test match against the British and Irish Lions after he was assessed to have picked up a head knock in the first half.
He failed to pass the concussion test on the sideline and sat out the rest of the game.
Hansen said yesterday Smith would go into concussion protocol this week but it was too early to say how long he would be out for.
''It is like any concussion. Until he goes through the protocols and passes them then he is not going to be available. It is day one and he is still to do anything in regard to testing. It is not the sort of thing you rush into. We'll give him a few days,'' Hansen said.
It was Smith's third concussion of the year and the second one in as many games.
He picked up one in the first game of the season for the Highlanders and then left the field on June 3 against the Crusaders, again for a head knock.
Hansen said the repeated concussions were a worry.
''There is obviously something going on there that is not quite right so we need to find out what that is.''
Chiefs dynamo Damian McKenzie has been called into the side to replace Smith. Midfield back Ryan Crotty strained a hamstring, also in the first half, and might make it back for the third test. He has been replaced in the squad by fellow Crusaders player Jack Goodhue.
Loose forward Matt Todd pulled a calf at training and has dropped out of the squad to be replaced by Akira Ioane.
Hansen has also decided to release four players to play for the Hurricanes tomorrow night against the Lions.
Highlanders loose forward Liam Squire is nearly back to full fitness and should be available for the third test.
Winger Julian Savea, midfielder Ngani Laumape, utility back Jordie Barrett and forward Vaea Fifita have all left the squad for the game but will come back in straight afterwards.
Hansen said it was simply a chance to get players to play games and also play against the Lions, which only happens once in a player's career.
Hansen also said hooker Dane Coles was free of concussion symptoms but there was no chance he would play against the Lions as he lacked match conditioning.
Coles' first appearance on the field could be for the Hurricanes in the playoffs.
Looking back on the match on Saturday night, won by the All Blacks 30-15, Hansen said it was a performance that was ''right up there'' by the side.
''But it is just the start. We have got a lot of work to do. They exposed us in a couple of areas. We did not connect that well in our kick, chase.
''They challenged us at lineout time and we challenged them. I thought both defensive lineouts were very good.''
He praised his side's discipline throughout the game.
''We talked about it before the test match in that we didn't want to give away stupid penalties.''
The All Black side transferred to Wellington yesterday and will spend the week in the capital.