The Pirates recalled Mattson from Triple-A Indianapolis on Saturday, Colin Beazley of the Pittsburgh Post-Gazette reports.
Mattson has given up four runs across his last two big-league appearances, but the Pirates will bring him back into their bullpen as the replacement for Antwone Kelly. Sporting a 4.93 ERA and 1.56 WHIP through 34.2 innings in the majors, Mattson will likely be limited to low-leverage work.