The Cardinals said Monday the right-hander has a torn ulnar collateral ligament, an injury that usually leads to Tommy John surgery.
The rocket-armed Hicks has hit 105 mph with fastballs this season and routinely reaches triple digits with his heater.
Hicks left Saturday's game against the Angels in the ninth inning after he had pitched 1 1/3 innings.
The 22-year-old Hicks is 2-2 with 14 saves and a 3.14 ERA in 29 games. He has struck out 31 in 28 2/3 innings.
Hicks made his big league debut last year, pitching in 73 games.
