The Pirates optioned Eisert to Triple-A Indianapolis on Friday, Danny Demilio of PittsburghBaseballNow.com reports.
The left-hander was called up by Pittsburgh on Tuesday and will return to Triple-A after firing 1.2 scoreless frames in two appearances. In 34 outings between the Pirates and White Sox this season, Eisert has a 6.00 ERA, 1.39 WHIP and 41:12 K:BB across 36 innings.