St. Louis Cardinals right-hander Riley O’Brien has sustained a mild right calf strain just weeks before he is scheduled to represent South Korea at the upcoming World Baseball Classic, casting doubt over his availability for the national team.
According to MLB.com, the 31-year-old reliever felt discomfort during a live bullpen session Saturday at the Cardinals’ spring training complex in Jupiter, Florida. O’Brien has not thrown off a mound since the incident but described the issue as minor.
“It felt better today than it did yesterday,” O’Brien said Tuesday, expressing optimism that the injury won’t sideline him long term.
The timing, however, is less than ideal. The WBC opens March 5 in Tokyo, with South Korea scheduled to play exhibition games in Osaka beforehand. Any extended downtime could jeopardize O’Brien’s role as the team’s projected closer.
Under WBC eligibility rules, players can represent a nation if one of their parents was born there. O’Brien, who is of Korean heritage, is one of four U.S.-born players selected by South Korea this year. He joins Jahmai Jones of the Detroit Tigers, Dane Dunning of the Seattle Mariners, and Shay Whitcomb of the Houston Astros.
South Korea manager Ryu Ji-hyun had already earmarked O’Brien for high-leverage duties, naming him the closer expected to handle critical moments from the seventh through ninth innings.
O’Brien is coming off a breakout 2025 campaign in which he posted a career-best 2.06 ERA across 42 appearances and collected six saves for St. Louis numbers that made him a key bullpen weapon both in MLB and for the national team.
If O’Brien is unable to recover in time, South Korea still has strong in-house options from the Korea Baseball Organization. Potential ninth-inning replacements include Park Yeong-hyun of the KT Wiz, Jo Byeong-hyeon of the SSG Landers, and You Young-chan of the LG Twins. Former LG closer Go Woo-suk who signed a minor league deal with Detroit in December is also considered a candidate.
Compounding matters, South Korea is already without two key starters. Moon Dong-ju of the Hanwha Eagles was sidelined due to a shoulder injury, while Won Tae-in of the Samsung Lions was recently withdrawn because of elbow issues.
