The Tigers assigned Mize to their minor-league camp Tuesday, Evan Woodbery of MLive.com reports.
Mize, the top overall pick in the 2018 first-year player draft, made two appearances in Grapefruit League play, giving up one run and striking out a pair of hitters over two innings. He'll likely open the 2019 campaign at Double-A Erie or High-A Lakeland.