Casas went 0-for-1 with a walk and a strikeout in Sunday's game against the Rays.
Casas made his debut in a major-league game, entering in the fifth inning for first baseman Mitch Moreland. Casas was Boston's first-round pick in 2018, then suffered a season-ending thumb injury two games into his professional career. He played third base in high school, but the organization is deep at that position, so expect to see more of the 6-foot-5, 240-pound Casas being exposed to first base.