Hicks underwent Tommy John surgery last June and could've potentially pitched at some point in 2020.
The 23-year-old Hicks also has Type 1 diabetes, according to Mark Saxon of The Athletic. Due to his status as an at-risk person, Hicks will be paid for 2020 and accrue service time despite opting out.
"We respect and understand Jordan's decision to opt out this season," Cardinals president of baseball operations John Mozeliak said, according to Mark Feinsand of MLB.com. "We wish him well as he continues his recovery from elbow surgery, and we look forward to seeing Jordan back on the mound for the 2021 season."
Prior to his injury, Hicks had developed a reputation for lighting up the radar gun with a sinker that regularly exceeded 100 mph.
In two seasons with the Cardinals, Hicks posted a 3.47 ERA with 101 strikeouts and 20 saves over 106 1/3 innings out of the bullpen. He opened the 2019 season as the team's closer until the elbow injury sidelined him. Giovanny Gallegos has since taken the reins in the ninth inning for the Redbirds.
By choosing to sit out, Hicks becomes the 13th major leaguer to opt out of the upcoming season, joining the likes of Buster Posey, David Price, and Michael Kopech.