Hansen aggravated a foot injury in Connacht’s 28-27 loss to the Bulls in the United Rugby Championship in Galway on Friday and will not travel with the squad on Tuesday as they prepare for the November 1 game at Soldier Field.
Aki and Henshaw will travel with the squad but Aki has a hip injury, although he also played for Connacht at the weekend, and Henshaw went off with a groin injury in Leinster’s 31-14 defeat by Munster in the URC in Dublin on Saturday.
Uncapped Munster forwards Edwin Edogbo and Brian Gleeson are also out of the squad because of injury but Jimmy O’Brien and Tom Farrell have been added to the travelling party.
Munster centre Farrell, 31, had a first international call-up six years ago in the Six Nations but did not play. O’Brien has 10 caps.
The pair will remain in the squad for the home tests against Japan, Australia and South Africa next month.