The Diamondbacks optioned Diaz to Triple-A Reno on Monday, Alex Weiner of ArizonaSports.com reports.
Diaz had three good starts at home and one poor start on the road during his first taste of the big leagues. While the overall impression was a favorable one, Diaz will head back to Reno for now. It's not clear yet how the Diamondbacks plan to fill Diaz's spot in the rotation this weekend, as Merrill Kelly (shoulder) and Eduardo Rodriguez (shoulder) won't be ready to return from the 60-day injured list.