On June 19, 2019, Contreras signed a minor league contract with the Milwaukee Brewers organization.[3] He split the campaign between the rookie–level Arizona League Brewers, Single–A Wisconsin Timber Rattlers, and Double–A Biloxi Shuckers. In 16 games split between the three affiliates, Contreras accumulated a 4–4 record and 2.86 ERA with 73 strikeouts across 50+1⁄3 innings pitched.[4] He did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[5]
Contreras returned to action with Biloxi in 2021, but only made 3 starts in which he logged a 5.19 ERA with 19 strikeouts.[6] In 2022, he made 35 appearances out of the bullpen for Biloxi and the Triple–A Nashville Sounds, compiling a 3.88 ERA with 73 strikeouts across 51 innings of work.[7]
Contreras split the 2023 campaign between Biloxi and Nashville, making 39 total appearances and registering a 4–3 record and 4.55 ERA with 90 strikeouts across 63+1⁄3 innings.[8] He elected free agency following the season on November 6, 2023.[9]
Houston Astros
Contreras signed a minor league contract with the Houston Astros on November 26, 2023.[10] In 19 games for the Triple–A Sugar Land Space Cowboys, he recorded a 1.40 ERA with 20 strikeouts across 19+1⁄3 innings pitched. On June 16, 2024, Contreras was selected to the 40-man roster and promoted to the major leagues for the first time.[11] On June 21, he was optioned back to Triple–A, without having appeared for the Astros, and briefly became a phantom ballplayer.[12] The following day, Contreras was recalled back to the major leagues.[13] He made his MLB debut on June 23.