Contreras was optioned to Triple-A Indianapolis on Thursday, Alex Stumpf of DKPittsburghSports.com reports.
The 21-year-old made his MLB debut Wednesday, tossing three scoreless innings against the Cubs while striking out four. He's one of the Pirates higher-ranked prospects, setting up a chance to be a part of the 2022 roster. Tanner Anderson had his contract selected Thursday and will take his spot on the roster.