Jupiter: Riley O'Brien, a reliever for the St. Louis Cardinals, is facing a calf injury that may hinder his participation in the upcoming World Baseball Classic (WBC) representing South Korea. O'Brien, who is eligible to play for South Korea due to his half-Korean heritage, sustained a mild right calf strain during a bullpen session at the Cardinals' spring training facility.

According to Yonhap News Agency, the injury was reported by MLB.com, noting that O'Brien has not pitched from the mound since the incident. The 31-year-old expressed optimism about his recovery, stating that his calf felt better than the previous day and hoping the injury would not be long-term. However, with the WBC commencing on March 5 in Tokyo and South Korea's preliminary games scheduled in Osaka, his readiness remains uncertain.

Under WBC eligibility criteria, players can represent a parent's country of birth even if they themselves were not born there. South Korea has included four U.S.-born players of Korean descent for the tournament, including O'Brien, Detroit Tigers outfielder Jahmai Jones, Seattle Mariners pitcher Dane Dunning, and Houston Astros utility player Shay Whitcomb.

South Korea's manager, Ryu Ji-hyun, has already designated O'Brien as the team's closer, expecting him to handle high-pressure situations from the seventh to ninth innings. O'Brien had a standout year in 2025, achieving a 2.06 ERA over 42 games and securing six saves for the Cardinals.

Should O'Brien be unable to participate, Ryu will need to select from KBO's top closers, such as KT Wiz's Park Yeong-hyun, SSG Landers' Jo Byeong-hyeon, and LG Twins' You Young-chan. Another potential option is former Twins closer Go Woo-suk, who recently signed with Detroit.

The South Korean team is already coping with the loss of two prominent starting pitchers. Moon Dong-ju of the Hanwha Eagles is sidelined due to a shoulder injury, and Samsung Lions' Won Tae-in was excluded from the roster owing to elbow issues.