Ioane suffered a shoulder rotator cuff injury in the narrow 22-17 victory over Scotland at Murrayfield on Saturday while Romano has a foot injury from the same game.
The All Blacks have already lost Dane Coles and Jerome Kaino to injury earlier in the tour.
Hansen said the 20-year-old Ioane, who has scored eight tries in 10 tests, would be sorely missed as the All Blacks sought to end their five-match tour unbeaten.
"He's a (World Rugby awards) rookie and player of the year nominee for a reason. He's played really, really well. But it's an exciting challenge for somebody to have to step up and do that job. I've got plenty of faith in the bloke we're going to probably pick. He's going all right, so we'll see how he goes," the All Blacks coach told reporters.
Matt Duffie, David Havili and Seta Tamanivalu are the options for Hansen on the wing while Scott Barrett and Patrick Tuipulotu are in line to replace Romano.
(Reporting by Mark Gleeson; Editing by Clare Fallon)
