Sims (elbow) will begin a rehab assignment with Triple-A Louisville on Tuesday.
Sims has been behind schedule since the start of camp after dealing with elbow and back issues over the winter, though the Reds never seemed to be concerned about any long-term absence. He looked like the favorite to close heading into spring training but was never officially named the closer, so his role upon his return is not yet clear. Tony Santillan and Art Warren have picked up the Reds' two saves so far this season.