The injury isn't considered serious, and he's expected to be back in the lineup on Friday.
"He tried to stretch, tried to get loose, but he's got stiffness in the back of his leg," manager Ron Gardenhire said. "So ... they're going to try to loosen him up, but he's not going to play."
Daniel Santana started in Casilla's place and batted second. The 21-year-old prospect hit .247 with seven homers, 15 doubles and five triples with Class A Beloit last season.
"People have been pumping [Santana] up down there," Gardenhire said. "He's a nice little player. We're going to get him out there and get a chance to take a look at him. I like that."
Fellow prospect Angel Morales started in right field and batted sixth. Morales, 22, dealt with an elbow injury last season and was limited to just 33 games with Class A Advanced Fort Myers, where he hit .264 with three homers and six doubles.
Santana went 2-for-5 with a walk but left the game in the ninth inning after dislocating his left pinkie sliding into second on a double. Morales went 2-for-3 with a double and two walks.