Duffy (back) was transferred to the 60-day injured list, Tony Andracki of Marquee Sports Network reports.
The move clears space on the 40-man roster for the Cubs to select Adam Morgan's contract. It doesn't look as though it will significantly impact Duffy's return date. He was previously thought to be on track to return around the All-Star break and will now be ineligible to come back before July 22, which may not wind up representing much more than a brief delay.