Casali was outrighted off the Rays' 40-man roster and elected to become a free agent, Marc Topkin of the Tampa Bay Times reports.
The 28-year-old backstop failed to break camp with the Rays and appeared in just nine major-league games last season. Casali has compiled an unremarkable .199/.285/.385 line in 161 games with the Rays over the last four years, so he'll likely be forced to settle for a minor-league deal in the offseason.