Blough was named the backup behind Matthew Stafford on Tuesday, Dave Birkett of the Detroit Free Press reports.
Josh Johnson was originally the backup behind Stafford, but the team released him Tuesday, leaving Blough as the No. 2. The Lions also signed Jeff Driskel to provide depth behind Blough and Stafford. Blough went undrafted out of Purdue in this year's draft after passing for 9,734 yards, 69 touchdowns and 43 interceptions in four years as a Boilermaker.