Del Castillo (shoulder) was placed on Triple-A Reno's 7-day injured list Saturday, Alex Weiner of ArizonaSports.com reports.
Del Castillo was diagnosed with a right shoulder strain, and he's expected to be out of action for at least a month, per Nick Piecoro of the Arizona Republic. Del Castillo was unable to crack the Diamondbacks' Opening Day roster after losing out to Jose Herrera for backup catching duties.