The Cardinals didn't disclose whether Hicks will undergo surgery, saying that they are "determining the next course of action."
Hicks suffered the right elbow injury during Saturday's 4-2 win over the Los Angeles Angels. He was removed in the ninth inning after 1 1/3 innings pitched.
The 22-year-old relief pitcher has excelled with the Cardinals this season, posting a 2-2 record with a 3.14 ERA, 0.94 WHIP and 31 strikeouts in 28 2/3 innings. He also has three holds and 14 saves in 15 chances with the club.
According to ESPN Stats & Information, Hicks has thrown 211 pitches at least 100 mph this season, over 100 more than the next-closest player. He became the only player in the last 10 years to throw 500 or more 100-mph pitches in a single season.
John Gant (three saves), Carlos Martinez (two saves) and Giovanny Gallegos are possible candidates to fill the Cardinals' closer role.