Yamamoto (shoulder) began a rehab assignment with the Mets' rookie-level Florida Complex League affiliate Friday, Anthony DiComo of MLB.com reports.
Yamamoto has been on the injured list since late May due to a sore right shoulder, but he resumed mound work in mid-July. The righty tossed a scoreless inning during his first rehab appearance and will likely require several appearances in the minors before he's ready to rejoin the major-league club. However, Yamamoto should be available as a starting option for the Mets if they need one in September.