D'Arcy faces six weeks on the sidelines after a scan revealed that he has suffered a stress injury to a bone in his foot. He will miss Ireland's games against Scotland, France and Italy.
"Following a scan yesterday afternoon it was confirmed that D'Arcy has a stress injury to a bone in his foot," the Irish Rugby Football Union said in a statement.
"The injury will require immobilisation in a boot for at least four weeks, with a projected return to play of six weeks, pending further tests and specialist review."
Ireland face Scotland in the Six Nations on February 24.