The 34-year-old Uehara has right elbow tendinitis. Baltimore's first Japanese-born player spent time on the DL earlier this season with a strained left hamstring.
Hernandez replaced Uehara as Baltimore's starter against the Washington Nationals on Sunday. Hernandez, a right-hander, went 1-1 with a 3.95 ERA in three appearances with the Orioles earlier this season.
Uehara is 2-4 with a 4.05 ERA. He is winless since April 13.