Yamamoto was recalled from Double-A Jacksonville ahead of his scheduled start Wednesday against the Cardinals, Jordan McPherson of the Miami Herald reports.
Yamamoto is poised to make his major-league debut in place of Jose Urena (back), who was placed on the injured list in a corresponding move. The 23-year-old right-hander has yet to pitch above Double-A, though he owns a respectable 3.58 ERA, 1.20 WHIP and 64:25 K:BB in 12 starts (65.1 innings) with Jacksonville this season. Whether he sticks in the rotation beyond Wednesday's start will likely depend on the severity of Urena's injury and how well Yamamoto performs in his debut.