On December 10, 2015, Hernández was selected with the 1st overall pick in the minor league phase of the Rule 5 draft by the Cincinnati Reds organization.

[4] He split the 2016 season between the Single-A Dayton Dragons and the High-A Daytona Tortugas, posting a cumulative 3–2 record and 2.18 ERA in 43 appearances.

He made his major league debut the next day, pitching 2 2/3 perfect innings with 5 strikeouts in an 11–7 loss to the Milwaukee Brewers.

[6] He split his rookie season between the Double-A Pensacola Blue Wahoos, the Triple-A Louisville Bats, and the Reds, recording a 5.18 ERA in 19 big league games with Cincinnati.

[7] On April 17, 2018, the Reds traded Hernández to the Los Angeles Dodgers in exchange for Zach Neal and Ibandel Isabel.

[8] He split time between the Double-A Tulsa Drillers and the Triple-A Oklahoma City Dodgers, posting a 4–2 record with 29 strikeouts between the two teams.

[9] On August 7, 2018, Hernández was claimed off waivers by the Milwaukee Brewers and assigned to the Triple-A Colorado Springs Sky Sox.