Alvarez was removed from Saturday's game against the Cubs with back spasms, Brian McTaggart of MLB.com reports.
Alvarez was visited by a trainer in the on-deck circle before his at-bat in the sixth inning, and he was pulled moments later after showing discomfort following a swing. It's unclear whether the 28-year-old's back will cause him to miss additional time, but the Astros could provide an update on his status in the near future.