Locke was recalled from Triple-A Indianapolis and right-hander Casey Sadler was optioned to the minor league team.
Locke was an NL All-Star last year and then faltered in the second half. He went 8-2 with a 2.15 ERA in 18 starts before the break, but just 2-5 with a 6.12 ERA after that.
This year, Locke was 0-1 with a 5.68 ERA in four starts for Indianapolis. He was limited to just two innings in spring training because of a strained oblique muscle.