"Tough decision, awesome guy," said Rays manager Kevin Cash, who noted the Rays might end up re-signing him. "Because he does provide some versatility. Left-handed bat and somewhat of a veteran presence. But the way he carried himself was great."
Casilla has a .247 average in nine Major League seasons with the Twins and Orioles.
Casilla was in the starting lineup for the Rays' split-squad game against the Red Sox on Tuesday prior to the announcement he had been released.
The Rays now have 33 players remaining in camp.
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.