Miller will join the Seattle rotation upon being promoted from Double-A Arkansas and is scheduled to make his first start Tuesday in Oakland, Corey Brock of The Athletic reports.
With Robbie Ray (elbow) done for the season and Easton McGee going on the injured list with a forearm strain after one turn as the Mariners' No. 5 starter, Seattle will turn to the 24-year-old Miller to fill the opening in the rotation. The right-hander is considered the best pitching prospect in the Mariners system, and he's coming off a start for Arkansas in which he allowed just one hit and one run while striking out five over five innings. Because of his inexperience, Miller's performance may have some volatility, but there's plenty of reward that comes with the risk he carries.