Vest will serve as the Tigers' opening pitcher for Sunday's game against the Diamondbacks, Evan Woodbery of MLive.com reports.
Vest hasn't recorded more than six outs in any of his 20 appearances on the season, so he's unlikely to work more than once through the order before giving way to Joey Wentz, who will work as a bulk reliever in his normal turn through the rotation. The 28-year-old Vest will be making his first start of the season and the third of his MLB career.