Inside The Cardinals

Cardinals 2025 Breakout Star Reportedly Sidelined Multiple Weeks

The St. Louis Cardinals reliever is working his way back into the fold.
Patrick McAvoy|
Aug 6, 2025; Los Angeles, California, USA; St. Louis Cardinals left fielder Lars Nootbaar (21) and relief pitcher Riley O'Brien (55) celebrate a win after defeating the Los Angeles Dodgers 5-3 at Dodger Stadium. Mandatory Credit: Kiyoshi Mio-Imagn Images
Aug 6, 2025; Los Angeles, California, USA; St. Louis Cardinals left fielder Lars Nootbaar (21) and relief pitcher Riley O'Brien (55) celebrate a win after defeating the Los Angeles Dodgers 5-3 at Dodger Stadium. Mandatory Credit: Kiyoshi Mio-Imagn Images | Kiyoshi Mio-Imagn Images

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St. Louis Cardinals

The St. Louis Cardinals aren't at full strength right now.

Cardinals reliever Riley O'Brien has been dealing with a calf injury in camp so far. On Friday, Derrick Goold of the St. Louis Post-Dispatch shared an update from manager Oli Marmol and noted that he will miss a few weeks of action, including at least the opening round of the World Baseball Classic.

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"Riley O'Brien is dealing with a mild right calf strain that will sideline him for a few weeks and force him to miss the opening round of WBC," Goold wrote. "He will remain on Korea's roster for possible addition later if team advances and he recovers, per [manager] Oli Marmol."

The Cardinals reliever is injured

St. Louis Cardinals relief pitcher Riley O'Brien
Sep 20, 2025; St. Louis, Missouri, USA; St. Louis Cardinals relief pitcher Riley O'Brien (55) pitches against the Milwaukee Brewers during the eighth inning at Busch Stadium. Mandatory Credit: Jeff Curry-Imagn Images | Jeff Curry-Imagn Images

O'Brien was a breakout star in 2025 for the Cardinals. He appeared in 42 games for St. Louis and logged a 2.06 ERA and 45-to-22 strikeout-to-walk ratio in 48 innings pitched. Before the 2025 season, O'Brien hadn't appeared in more than eight games in a big league season in his young career so far. St. Louis gave him a big opportunity in 2025 and he made the most of it.

When the 2026 season kicks off, O'Brien is going to be an important piece for this bullpen. Last year, it wasn't clear if he would play a big role at this time. Now, the expectation heading into the season is that he will but this is an injury to watch out for now.

The Cardinals' bullpen looks different now than at this point last year, to say the least. Ryan Helsley, Phil Maton and Steven Matz are all pitching elsewhere. Guys like O'Brien and JoJo Romero are in line for bigger roles and the club brought in guys, like Ryne Stanek and Justin Bruihl.

As Spring Training continues, we'll continue to keep an eye on O'Brien, and all of the other injuries in camp. As more information is provided about O'Brien's calf injury, we will update here. Calf injuries are tough, so this is something to monitor.

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Patrick McAvoy
PATRICK MCAVOY

Patrick McAvoy's experiences include local and national sports coverage at the New England Sports Network with a focus on baseball and basketball. Outside of journalism, Patrick also is pursuing an MBA at Brandeis University. After quickly rising as one of the most productive writers on the site, he expanded his reach to write for Baseball Essential, a national baseball site in Sports Illustrated Media Group. For all business/marketing inquiries regarding Inside The Cardinals, please reach out to Scott Neville: nevilles@merrimack.edu

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