The Red Sox placed Gasper on the 10-day injured list Sunday, retroactive to Sept. 26, with a right biceps strain.
Gasper was hurt on a swinging strikeout during the first game of Friday's doubleheader against the Cubs, and the injury has been deemed significant. Boston is expected to be without Gasper for at least the wild-card round and could be without his services for the entire postseason. He ends the regular season having hit 10 homers with an .823 OPS across 225 MLB plate appearances.