Hernandez (calf) is beginning a rehab assignment Tuesday with Triple-A Indianapolis, Kevin Gorman of TribLive.com reports.
Hernandez should be able to return to the Pirates' bullpen by the weekend, after making maybe one or two appearances on the farm. The 25-year-old had posted a strong 2.63 ERA and 28:6 K:BB in 27.1 innings before he landed on the injured list June 18 with a right calf strain.