Diaz was placed on the 7-day injured list at Triple-A Reno on Thursday due to a blister on his right hand, Jesse Friedman of GoPHNX.com reports.
Diaz is expected to miss just one start with the issue. The young right-hander held a solid 4.05 ERA, 1.30 WHIP and 14:8 K:BB in 20 innings covering three starts for Arizona last month, but with Eduardo Rodriguez back and Merrill Kelly's (shoulder) return imminent, Diaz probably wasn't going to be back in the majors anytime soon even if he was healthy.