Kieran Read has been ruled out of New Zealand's Test against England this weekend after signs of his concussion reemerged.
The IRB Player of the Year has struggled with concussion issues since a knock to the head back in Round 10 of Super Rugby kept him off the field for six weeks.
He returned against the Force last week but has suffered a recurrence of the symptoms that kept him on the sidelines.
Try-scoring machine Julian Savea is also a doubt for the All Blacks ahead of facing a depleted England side in Auckland.
"We're not prepared to risk him playing and that's our decision, not his, and we'll progress that day by day," Hansen said of Read's situation.
"Long term I'm not too concerned, but we're just not prepared risk him this week.
"He's frustrated, as you would be, but we're very lucky we've got capable people who can fill his place.
"Jerome Kaino and Victor Vito have been performing very well and Liam Messam is an incumbent. We've got some good people to step up."
Sam Cane could be miss the entire Test series with a knee injury, hence the call up for Matt Todd on Monday, with Steven Luatua also joining the group to cover for Read.
"Losing players is only disruptive if we allow it to be. Rugby is a contact sport, we're going to have people get injured and we just have to deal with that," said Hansen.