Oct 4, 2015; Atlanta, GA, USA; Detailed view of St. Louis Cardinals hat and glove in the dugout against the Atlanta Braves in the ninth inning at Turner Field. The Braves defeated the Cardinals 2-0. Mandatory Credit: Brett Davis-Imagn Images Brett Davis-Imagn Images

Cardinals Shutting Down 30-Year-Old Breakout Star

Originally posted on St. Louis Cardinals on SI
By Patrick McAvoy | Last updated Sep 1, 2025 2:18 PM ET

The St. Louis Cardinals have one of the best bullpens in baseball but it is taking a significant hit.

30-year-old right-handed pitcher Riley O'Brien has broken out this year for St. Louis. He has a 1.69 ERA and 35-to-17 strikeout-to-ratio in 37 1/3 innings pitched. Since Ryan Helsley, Steven Matz, and Phil Maton got traded, O'Brien has been a guy that has helped keep the bullpen together for St. Louis. Since the trade deadline, O'Brien has made nine appearances and pitched to a 1.74 ERA and 6-for-4 strikeout-to-walk ratio in 10 1/3 innings pitched.

Unfortunately, he was shut down by the team on Monday due to shoulder soreness, as shared on social media by MLB.com's John Denton.

The Cardinals got some bad news about a breakout star on Monday

Jeff Curry-Imagn Images

"Cardinals RHP Riley O’Brien underwent an MRI on his sore right shoulder this morning and is shut down for the time being until a course of action is set," Denton said. "This has been a breakout season for O’Brien, who has been counted on in high-leverage spots and in closing roles."

Before the 2025 season, O'Brien had pitched in just 10 big league games. Over that stretch, he had 10.45 ERA.

Down in the minors this year, O'Brien had a 2.79 ERA as well with the Triple-A Memphis Redbirds. Clearly, the Cardinals have unlocked something in the righty but now it's unclear if he will return this season. With just 24 games left in the 2025 season, there isn't a ton of time left to go through an entire Injured List stint as well as the buildup to get back onto the rubber. There at least is a chance that we have seen O'Brien's final appearance with the club for the 2025 season, but that part is speculation.

If O'Brien does end up being done for the season, this campaign was a great tryout to make it clear that he should be a part of the Cardinals' bullpen when the 2026 season gets here in the spring. Hopefully, we'll see him again this season, though.

This article first appeared on St. Louis Cardinals on SI and was syndicated with permission.

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