Triple-A Worcester placed Downs (ankle) on its 7-day injured list Thursday.
Downs hadn't played for Worcester since Aug. 18 with a left ankle injury before being deactivated a week later. The 24-year-old debuted in the majors earlier this season and hit .154 over 14 games, but his ankle injury may take a promotion back to Boston off the table when the active roster expands to 28 men in September.