Relief pitcher Riley O’Brien, a half-Korean right-hander currently with the St. Louis Cardinals, has encountered an untimely setback just weeks before he was expected to represent South Korea at the upcoming World Baseball Classic.
The 31-year-old reliever, who had been penciled in for a critical late-inning role on the national team, is now dealing with a calf injury that could jeopardize his participation in the global tournament. His situation adds to a growing list of concerns for South Korea, which is already preparing to compete without several prominent arms due to injury.
According to a report published Tuesday by MLB.com, O’Brien sustained what he described as a mild strain in his right calf during a live bullpen session over the weekend. The incident occurred Saturday at the Cardinals’ spring training complex in Jupiter, Florida, where the club has been conducting preseason workouts in preparation for the upcoming Major League Baseball campaign. Since that session, O’Brien has not thrown off a mound, an indication that the team is exercising caution as they evaluate the severity of the issue.
While speaking about the injury, O’Brien struck a cautiously optimistic tone. He noted that the discomfort had improved from one day to the next, suggesting that the strain might not develop into a prolonged absence. “It felt better today than it did yesterday,” he said Tuesday. “Hopefully, it’s nothing too long-term.” Even so, with the international tournament rapidly approaching, any interruption to his throwing schedule could complicate his readiness.
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The timing could hardly be worse. The World Baseball Classic is scheduled to begin March 5 in Tokyo, with South Korea set to play a series of exhibition games in Osaka in the days leading up to the tournament.
Those tune-up contests are intended to help the team refine its pitching rotation and bullpen hierarchy before facing top international competition. If O’Brien is unable to resume mound work soon, he may not have sufficient time to ramp up safely for game action, potentially forcing South Korea to adjust its bullpen plans at the last minute.
O’Brien’s inclusion on the roster was particularly noteworthy because of his unique background and the flexibility provided by WBC eligibility rules. Under tournament guidelines, players are permitted to represent a country if one of their parents was born there, even if the player himself was born elsewhere. That provision has allowed several U.S.-born players of Korean descent to join South Korea’s squad this year, strengthening ties between Korean baseball and the Korean-American community.
In addition to O’Brien, South Korea selected three other U.S.-born players with Korean heritage. Those players include outfielder Jahmai Jones of the Detroit Tigers, right-handed pitcher Dane Dunning of the Seattle Mariners, and utility player Shay Whitcomb of the Houston Astros. The quartet represents a strategic effort by the Korean Baseball Organization and national team leadership to expand the talent pool and integrate players competing at the highest professional level in the United States.
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Manager Ryu Ji-hyun had already expressed strong confidence in O’Brien’s ability to anchor the bullpen. He publicly named the veteran reliever as South Korea’s closer for the tournament, outlining a plan to deploy him in high-leverage situations anywhere from the seventh inning through the ninth. Rather than reserving him strictly for traditional save opportunities, Ryu envisioned a flexible approach, using O’Brien whenever the game’s most pivotal moments arose.
That trust was rooted in O’Brien’s outstanding performance during the 2025 MLB season. Pitching in 42 games for the Cardinals, he posted a career-best 2.06 earned run average while collecting six saves. Beyond the raw numbers, he demonstrated an ability to handle pressure situations and retire hitters in critical spots, attributes that are invaluable in a short tournament format like the WBC.
In such competitions, where every game carries significant weight and one misstep can derail championship aspirations, dependable late-inning relief is often the difference between advancement and early elimination.
Should O’Brien ultimately be ruled out, Ryu Ji-hyun will be forced to pivot to alternative options. Fortunately, South Korea still boasts several accomplished closers within the Korea Baseball Organization (KBO). Among them is Park Yeong-hyun of the KT Wiz, an All-Star caliber reliever known for his poise and power repertoire.
Another candidate is Jo Byeong-hyeon of the SSG Landers, who has established himself as a reliable ninth-inning presence in domestic competition. Additionally, You Young-chan of the LG Twins offers experience and consistency in late-game scenarios.
There is also the intriguing possibility of turning to Go Woo-suk, the former closer for the LG Twins who signed a minor league contract with the Detroit Tigers in December. Although he has since transitioned to the U.S. professional system, Go remains eligible for selection and could provide valuable closing experience if called upon. His familiarity with international competition and prior success in high-stakes games might make him an appealing fallback option.
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The broader concern for South Korea extends beyond the bullpen. The team has already suffered significant losses in its starting rotation. Moon Dong-ju, the hard-throwing ace of the Hanwha Eagles, was omitted from the roster because of a shoulder injury that has prevented him from ramping up fully. His absence removes one of the nation’s most electric young arms from the equation.
Meanwhile, Won Tae-in of the Samsung Lions was scratched from the team on Sunday due to elbow issues. Losing two frontline starters significantly reshapes the pitching blueprint heading into international play.
These setbacks place additional importance on the bullpen’s stability. In tournament settings, managers often rely heavily on relievers to bridge gaps or cover shortened outings by starters who may not yet be fully stretched out in early March. With two key starters sidelined, South Korea could lean even more on its relief corps to navigate high-pressure innings against formidable opponents.
O’Brien’s potential absence, therefore, carries ramifications beyond simply replacing one pitcher. It could alter bullpen roles, impact matchup strategies, and influence how aggressively Ryu manages his rotation. If the team must turn to a KBO closer in the ninth inning, it may adjust earlier-inning usage patterns accordingly. Every decision will be magnified in the compact schedule of the WBC.
For O’Brien personally, the opportunity to pitch for South Korea represents both a professional milestone and a meaningful connection to his heritage. Representing a parent’s country on a global stage often holds deep emotional significance for players in the diaspora. The chance to wear the national uniform in Tokyo, before passionate fans, and compete against the world’s elite talent is an experience few athletes forget. That possibility now hinges on the recovery of his right calf over the coming days.
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The Cardinals, for their part, will also be monitoring his progress closely. While international play is a source of pride, MLB clubs are understandably cautious about player health during spring training. Ensuring that O’Brien enters the 2026 season healthy is a priority for St. Louis, particularly after his breakout performance the previous year. A careful rehabilitation approach may be necessary, even if it complicates his WBC timeline.
Ultimately, the next several days will be critical. If O’Brien can resume throwing off a mound without discomfort and gradually build up his workload, he may still be able to join South Korea in time for the tournament. If not, Ryu Ji-hyun and his staff will need to finalize contingency plans and entrust the closing duties to another proven arm.
As South Korea prepares for the World Baseball Classic amid mounting pitching concerns, O’Brien’s recovery becomes one of the team’s most closely watched storylines. His status will likely remain uncertain until he demonstrates full mobility and mound readiness. For now, both the Cardinals and the Korean national team can only hope that what he termed a “mild” strain proves to be just that — a brief interruption rather than a tournament-altering setback.
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