Baez was optioned to Double-A Midland on Sunday.
Baez will head to Double-A after tossing a scoreless inning, striking out two batters and hitting another, in his only appearance with the Athletics during spring training. The 23-year-old combined to produce a 2.36 ERA with 101 strikeouts over 110.2 innings in 24 starts with Double-A San Antonio and Double-A Midland last season.