Turnbull (neck) had his rehab assignment transferred to Triple-A Toledo on Friday.
The right-hander made a couple rehab starts for High-A West Michigan, most recently covering three innings with two runs allowed and four strikeouts. He's been cleared to jump up the ladder to Toledo, which leaves Turnbull just one step away from a return to the majors. He got off to a rough start in his return from Tommy John surgery (7.26 ERA), but he figures to get another chance to prove himself in the Detroit rotation, likely bumping aside Joey Wentz once he's deemed ready for activation.