The Pirates recalled Eisert from Triple-A Indianapolis on Tuesday.
After being optioned to Triple-A on Friday, Eisert will now rejoin the big club to replace the injured Isaac Mattson (hip). Eisert hasn't been very effective in the majors this season, posting a 6.00 ERA and 1.39 WHIP across 36 frames and will likely be reserved for low-leverage situations as long as he's with Pittsburgh.