Sosa was optioned to High-A Palm Beach on Monday, Jenifer Langosch of MLB.com reports.
Sosa was another Cardinals prospect that needed to be added to the 40-man roster for Rule 5 protection, although he won't be an option for the big league team anytime soon. He'll start the season in High-A, where he slashed .294/.314/.412 in 34 at-bats to end 2016.