An MRI revealed a torn right thumb ligament on Casilla, who has helped spark the Twins this season by hitting .313. Casilla will see a doctor on Wednesday to determine the extent of the tear and the team will then determine how long he will be out.
Everett returned from his rehab assignment on Tuesday and was initially asked to accept a demotion to Triple-A Rochester. Casilla's injury now leaves a spot on the big league roster for the veteran shortstop.
"We need middle guys," Minnesota manager Ron Gardenhire said. "That's what we signed him for. He's been playing and he's ready to go."
Everett has been out since May 22 with a shoulder injury and has hit .189 in 25 games with the Twins this season. He signed a one-year, $2.6 million contract during the offseason.