The Diamondbacks optioned Del Castillo to Triple-A Reno on Monday.
Del Castillo slugged a home run in his last start Saturday versus the Brewers, but he has posted a weak .555 OPS over 164 plate appearances on the season. With James McCann (quadriceps) returning from the injured list to resume duties as Arizona's backup catcher, Del Castillo will head back to Reno.