The Reds placed Santillan on the 15-day injured list Friday with an oblique strain, Charlie Goldsmith of Fox 19 Now Cincinnati reports.
It's unclear when he was hurt, but Santillan last pitched Monday versus the Brewers. The right-hander had stabilized the Reds' closer job of late, turning in a 1.13 ERA and 6:1 K:BB over his last eight innings while notching three saves. Though he will be eligible for activation July 8, Santillan could be held out until after the All-Star break, given the nature of the injury. Emilio Pagan (hamstring) is on a rehab assignment and is likely to retake the Reds' closer job before Santillan returns from the IL.