Hernandez allowed at least one earned run in 10 of his last 12 outings and gave up home runs in his last three appearances.
Hernandez, 34, is a 10-year big leaguer. This was his second season in Cincinnati.
Sal Romano was promoted from Triple-A Louisville to take the place of Hernandez in the bullpen. Romano was 4-7 with 4.55 ERA in 37 games.