Martin was optioned to Triple-A Round Rock on Wednesday.
Martin lost out on playing time recently and was in the lineup for just one of the last six games. The 26-year-old was recalled in late July and hit .240 with five homers, three doubles, 13 RBI, 12 runs and a stolen base across 32 games. He should see more consistent at-bats in the minors, while his demotion will help make room for Willie Calhoun (forearm), who was reinstated from the 60-day injured list Wednesday.