Santillan (oblique) will begin a rehab assignment with Triple-A Louisville on Friday.
Santillan is finally ready to pitch in games again after being sidelined since late June with a severe left oblique strain. Because he's missed so much time, he likely will require a handful of rehab outings before being reinstated to the Reds' active roster. Santillan will be slated for a setup role with the Reds as long as Emilio Pagan's hand issue doesn't linger.