The team placed Steve Clevenger on 15-day disabled list with a right oblique strain. The move is retroactive April 26).
Castillo is available for Saturday's game against the Philadelphia Phillies at Citizens Bank Park.
Castillo, 25, is batting .320 with two home runs and eight RBIs along with a .435 on-base percentage for Triple-A Iowa. A September callup last season, Castillo batted .154 in four games with the Cubs.
Clevenger edged out Castillo for the backup job behind Geovany Soto, who has struggled this season, batting .140 with a home run and one RBI. Clevenger is batting .500 (11-for-22) this season.