Diego Brandao has agreed to replace Miller, UFC officials announced on Tuesday. The bout will headline the UFC Fight Night, which takes place at The 02 in Dublin.
Miller (21-8) suffered torn ligaments in his thumb, according to the UFC. There is no timetable for his return.
McGregor (14-2) has not fought since August, when he tore his ACL in a unanimous decision win over Max Holloway. The 25-year-old Irishman is 2-0 in the UFC, with wins over Holloway and Marcus Brimage.
For Brandao (18-9), the fight will mark his first appearance of 2014. He was supposed to face Will Chope in March, but the fight was ultimately canceled. He was then scheduled to fight Brian Ortega on May 31, but withdrew late due to injury.
The Brazilian featherweight suffered a first-round knockout loss to Dustin Poirier in December. The loss snapped a three-fight win streak.