Casilla was the starting second baseman out of spring training, but he slumped badly early in the season and fell out of favor with manager Ron Gardenhire for his sloppy play.
In two stints with the Twins this year, he is hitting .180 with three doubles and five RBIs. After being sent down to Rochester on June 11 for a wakeup call, Casilla hit .340 with two homers and 17 RBIs in 40 games for the Red Wings.
To make room on the roster, the Twins will send infielder Matt Tolbert to Rochester. The move will be made official on Friday after the All-Star break.