The Pirates optioned Mattson to Triple-A Indianapolis on Wednesday, Kevin Gorman of TribLive.com reports.
Mattson (1.2 innings, 39 pitches) and Brandon Eisert (2.1 innings, 41 pitches) both saw heavy usage out of the bullpen in Tuesday's 8-7 loss to Arizona in 12 innings, so Pittsburgh will call up a pair of fresh relief arms from Triple-A (Noah Murdock and Hunter Barco) to replace them ahead of Wednesday's series finale. During his six-plus-week stay in the majors, Mattson appeared in 13 games and turned in a 6.39 ERA, 1.74 WHIP and 15:4 K:BB across 12.2 innings.