Manager Bud Black says Morrow felt discomfort in the shoulder during Sunday's rehab start with Double-A San Antonio. Black described the discomfort as a setback. Black said Morrow has returned to San Diego, where he was to have a MRI on the shoulder.
Morrow was 2-0 with a 2.73 ERA in five starts before he was placed on the 15-day disabled list on May 5, retroactive to May 3. He signed with the Padres as a free agent following five seasons with Toronto.
He was 1-3 with a 5.67 ERA with Toronto in 2014, when he missed the majority of the season with a finger injury.