Walker was recalled from Triple-A Sacramento prior to Monday's game against the Reds, Shayna Rubin of the San Francisco Chronicle reports.
Walker will receive another opportunity in the major leagues after he was optioned July 9. He's been solid at Triple-A Sacramento in 12 appearances since his demotion, working to a 1.47 ERA and 0.93 with a 19:6 K:BB across 18.1 innings.