The 22-year-old Hicks was diagnosed with a torn ulnar collateral ligament on Monday following an MRI. Hicks was previously diagnosed with tendinitis in his right triceps.
Hicks was 2-2 with a 3.14 ERA in 29 games this season for the Cardinals. He had 14 saves in 15 opportunities.
John Mozeliak, the president of baseball operations for the Cardinals, said Dr. George Paletta will perform the surgery Wednesday morning in St. Louis.
"Needless to stay, it's very disappointing,'' Mozeliak said. "Certainly, he'll be missed. We were overly optimistic on this. Then the dark clouds moved in.''
Hicks will miss the rest of this season and likely part of the 2020 season. The club will get a more definite timeline once Hicks is done with surgery and moves on to rehab, Mozeliak said.
"I want to come back strong. I want to play a long time,'' Hicks said. "My mentality is to stay strong in my head, work hard and get back.''
In his 29 games this season, Hicks struck out 31 and walked 11 in his 28 2/3 innings.
Manager Mike Shildt said he has had good conversations with Hicks in the past two days.
"I don't feel good about it but he feels good moving forward,'' Shildt said. "This team is a tough, resilient team. We get it and our job is to figure it out. Move forward. Next man up. Be there to support Jordan.
"It's discouraging to have this happen to him. To come this far and have a setback is tough. He'll be better for it. Maybe he comes back and throws 108 (mph).''
Hicks left Saturday's game against the visiting Angels in the ninth inning.
"I felt different obviously,'' Hicks said. "I knew a MRI would show the true results.''
Hicks sat in the Cardinals dugout for about five minutes answering questions before the Cardinals met the Oakland Athletics in a two-game series.
"I'm good right now, staying positive,'' Hicks said. "I'll have surgery tomorrow (Wednesday) and get it done. I'm optimistic about the process. I'm in a good place right now.''
Shildt believes Hicks will come back and be just as good.
"He's taken multiple steps this season to get better,'' Shildt said. "He was more under control. There was more efficiency in his delivery. Jordan threw a lot of strikes. He's a tough guy to be in a hole against. He just grew right before our eyes. He went from relying on his talent to developing his talent. He's impressive.''
The hard-throwing righty owns the 21 fastest pitches thrown this year in the majors, with the top pitch at 104.3 mph.
Hicks has thrown 211 pitches at least 100 mph this season, over 100 more than the next-closest player. Last year, Hicks threw 673 100 mph pitches and became the only player in the past 10 years to throw 500 or more 100 mph pitches in a single season.
But Hicks said he did not think throwing hard contributed to his injury.
"Honestly, I don't know what it stems from,'' Hicks said. "That's how I pitch. Whatever comes with that, comes with it. Tommy John is not about how hard you throw. It's part of this game.''
Hicks made his big league debut last year, pitching in 73 games.
The Cardinals will use former starter Carlos Martinez as the main closer. He has made 13 appearances since returning from the injured list on May 17 after being out with a right shoulder strain. Martinez (1-0) has two saves in four opportunities.
"The comfort level is to go with Martinez. The good news is we have some depth there,'' Mozeliak said about the bullpen. "Hopefully, we can absorb it. No doubt though, it's a loss.''
Shildt believes Martinez will do well in his new assignment.
"It's a natural progression for Carlos,'' Shildt said. "It's not foreign to him. He's built for it not only in his competitive spirit, but in his desire to seek big moments and execute a lot of plus pitches.''
"I don't think anyone will be throwing us a pity party,'' Mozeliak said. "We'll move on.''
With the July 31 trade deadline approaching, Mozeliak said the team's focus will likely remain the same.
"It seems like you're always looking to add pitching,'' Mozeliak said. "Today's news doesn't help in that regard or change how we're thinking. We'll make that decision as we get closer.''
The Cardinals recalled right-handed pitchers Daniel Ponce de Leon and Dominic Leone from Triple-A Memphis. The team also announced that left-handed pitcher Genesis Cabrera was optioned to Memphis.
Ponce de Leon, who worked six scoreless innings in a start last Wednesday against Miami, is being recalled for a third time this season. He has a 1.20 ERA in three starts (15 innings) for St. Louis this season.
Leone, who was optioned to Memphis on May 17, has appeared in 13 games for the Triple-A Redbirds, with a 4.19 ERA in 13 games.
The Associated Press contributed to this report.