Cardinals Promote No. 18 Prospect to Back Up Kyle Leahy

The Cardinals are getting a reinforcement

Peoria Chiefs pitcher Cooper Hjerpe throws against Dayton on Tuesday, May 9, 2023 at Dozer Park in Peoria. | USA TODAY Network via Reuters Connect

The St. Louis Cardinals have been a little short on pitching since the loss of Hunter Dobbins for the season. To make matters worse, right-hander Kyle Leahy, who is starting on Sunday against the Colorado Rockies, has been placed on an innings limit for the rest of the season, so the Cardinals needed some reinforcements.

Fortunately, they have found one. On X, the team announced that it had promoted left-hander and No. 18 prospect Cooper Hjerpe to the major leagues as a piggyback option for Leahy for Sunday's game

Leahy pitched just three innings in his last start, so adding some depth is important for the Cardinals.

Welcome to the Show, Cooper!

We have recalled LHP Cooper Hjerpe from Memphis (AAA). He will wear number 56. pic.twitter.com/aFR0LdnNEY

— St. Louis Cardinals (@Cardinals) September 6, 2026

Cardinals call up Cooper Hjerpe

Jun 12, 2022; Corvallis, OR, USA; Oregon State Beavers pitcher Cooper Hjerpe (26) delivers a pitch in the 1st inning during Game 2 of a NCAA Super Regional game at Coleman Field. Mandatory Credit: Soobum Im-USA TODAY Sports | USA TODAY Sports

Hjerpe, 25, was the Cardinals first-round draft pick back in 2022 out of Oregon State University. He has dealt with several arm injuries over the course of his minor league career, even missing the entire 2025 season. But he has finally gotten healthy in 2026.

In 15 starts across four minor league levels, the left-hander is 0-1 with a 3.00 ERA, a 1.26 WHIP and a .151 opponent batting average. The Cardinals needed some pitching depth, and now, they have one more option for depth as they prepare for the rest of the season and try to take some momentum into 2027.

With Dobbins out, the Cardinals were in need of an extra arm in the system that can be used on the major league roster and can be ready to go in case something goes wrong in 2027. The Cardinals have done a fantastic job of accumulating pitching depth under Chaim Bloom, and though Hjerpe was drafted by John Mozeliak in 2022, he is now major league ready and is somebody that can be plugged in when need be.

The Cardinals could also potentially convert a reliever to the rotation at some point, but the important thing is that they have insurance behind Leahy if he cannot go deep into the game on Sunday, or perhaps in any of his remaining starts this season.

This allows the Cardinals to keep Leahy fresh for the future and preserve his arm in a rebuilding year. It will be interesting to see if Hjerpe can catch on quick and become a valuable piece of the Cardinals pitching staff. He is somebody who could start in the future, but the Cardinals at least have some more depth on the big-league roster.