Santander then took some time off to rest before putting the bat back in his hands, but the pain remained.
An MRI then revealed the torn labrum. The injury was made public on Day 1 of spring training.
The 31-year-old Santander missed most of last season while rehabbing the same left shoulder, appearing in just 54 regular-season games and five more in the post-season.
He is entering the second of a five-year, $92.5-million contract signed with the Blue Jays ahead of last season.