The Reds transferred Santillan (back) to the 60-day injured list Tuesday.
The move guarantees Santillan will return from his back strain no sooner than mid-August, though manager David Bell speculated the reliever might not be activated until September, per Charlie Goldsmith of The Cincinnati Enquirer. Prior to landing on the shelf with al lower-back strain, Santillan struggled to the tune of a 5.49 ERA and 1.78 WHIP in 19.2 innings, but he could still see high-leverage work once healthy.