4 pitchers who could replace Miles Mikolas in the Cardinals rotation

RHP Kyle Leahy

I list Kyle Leahy first because he's probably the best (and most likely) challenger for Mikolas's spot in the rotation should the veteran be released. Leahy is by no means a prospect; he's 28 years old. However, he is still relatively new to the majors. He's thrown only 113 professional innings, and he has a career 3.50 ERA in the majors.

As a prospect, Leahy was nothing special. He had a 5.51 ERA in the minors across 524.1 innings. He struck out only 479 batters in that time, and his 1.604 WHIP wasn't inspiring. Leahy got a cup of coffee with the Cardinals in 2023, and he allowed four runs in only 1.2 innings that year.

His second audition in 2024 was better, as he finished the year with a 4.07 ERA in 48.2 innings of relief. He finished 14 games last year, and his comfort with high-leverage situations was growing.

Fast forward to 2025, and Kyle Leahy has been one of the most complete relievers for manager Oliver Marmol and the Cardinals. He has a 2.59 ERA in 62.2 innings (45 games). He's struck out 55 batters, and his 1.07 WHIP is stellar.

Leahy started the year off strong with a 1.02 ERA in 17.2 innings in the month of April. He was roughed up in May and June with ERAs of 3.00 and 4.40, respectively. Since then, Leahy has righted the ship. He finished July with a 2.63 ERA in 13.2 innings (16 strikeouts), and his August has been even hotter. He hasn't allowed a run this month through 4.1 innings, and he's struck out 5 batters, most notably four in his recent appearance against the Los Angeles Dodgers when he struck out Will Smith, Teoscar Hernandez, Andy Pages, and Miguel Rojas.

Kyle Leahy probably isn't stretched out enough right now to go five or six innings, but he could easily throw 60 pitches in an outing given sufficient rest. He should immediately take Miles Mikolas's next turn in the rotation to help the Cardinals down the stretch. Consider it his audition for the 2026 starting rotation.