Injured flyhalf Dan Carter would also miss the rest of the Rugby Championship season and would make his return from a broken leg through New Zealand's provincial championship, Hansen added.
The 32-year-old Nonu broke his arm during the first half of the All Blacks' 14-10 Rugby Championship victory over South Africa on Saturday. He did not appear in the second half and was replaced by Ben Smith at inside centre.
"Ma'a has just come out of having an operation on his arm. It's broken, he has got a plate in it so that'll be his season and he'll back for the Hurricanes," Hansen told reporters at the team hotel in central Wellington.
"It's disappointing for him and for us but it creates an opportunity for someone like Ryan Crotty when he is all cleared to play and for Malakai (Fekitoa) for that matter."
The absence of the 94-test veteran for the remainder of the season should effectively ensure that code switcher Sonny Bill Williams will be guaranteed a spot on the end-of-year tour to the United States and Britain.
Hansen had sought dispensation from the New Zealand Rugby Union board to select Williams, who is still contracted to Australia's National Rugby League club Sydney Roosters, on the tour.
NZRU rules state that a player must appear for a team in a New Zealand domestic-based competition before becoming eligible for the national side, though Williams' rugby league duties are expected to preclude that before the All Blacks head overseas.
OPENED DOOR
The 2011 World Cup winner is officially joining the Waikato Chiefs next season with the hope of making his second successive rugby union global showpiece and possibly pushing for a spot in the All Blacks sevens for the 2016 Rio Olympics.
Hansen was non-committal when asked directly about Williams, only saying that Nonu's injury had opened the door for his possible selection.
The 32-year-old Carter has not played a test for the All Blacks since his 100th appearance last November against England due to a NZRU-approved six-month sabbatical that ended after the three-test series against England in June.
Carter then broke his leg in the Super Rugby final against the New South Wales Waratahs and while he had initially hoped to have been out for about a month, he told local media last month he was hoping to be available for the final two Rugby Championship clashes in Argentina and South Africa.
Hansen, however, said on Sunday that Carter would slowly build back into match fitness with Canterbury in the provincial competition and he hoped he would be available for the All Black's third Bledisloe Cup clash with Australia on Oct. 18.
"Dan will play (provincial rugby) and have a graduated programme," Hansen said.
"Whether that's 40 or 60 minutes and then graduating to a full 80 the following week with the idea being that he would be available for the Brisbane test."
The All Blacks have already retained the Bledisloe Cup after drawing against Australia in Sydney last month before recording a thumping victory over the Wallabies a week later.
