León made his professional baseball debut as a 17-year-old with the Saraperos de Saltillo of the Mexican League in 2006, pitching in 4 games as a reliever.

He then played in 30 games for the Tomateros de Culiacán of the Mexican Pacific League, pitching to a 6–0 record, 3.49 ERA, and 27 strikeouts in 281⁄3 innings.

[1] The Oakland Athletics purchased León's contract before the start of the 2008 minor league season, and he was assigned to the Advanced-A Stockton Ports.

León was assigned back to Saltillo on June 24, 2008, and played the rest of the minor league season there, going 2–1 with a 4.30 ERA in 13 games.

[1] In 2010, he would pitch in 3 games for Midland before being placed on the disabled list, and would then undergo Tommy John surgery that would sideline him for the rest of the season.

In a first-round game against the Canada national baseball team, he started a brawl after hitting Rene Tosoni with a pitch following a bunt single by Chris Robinson.

[1] León played the entire 2014 season with Triple-A Sacramento, posting a 10–7 record, 4.97 ERA, and 128 strikeouts in 145 innings pitched.