Walker struck out one in a scoreless inning during Friday's 5-1 loss to the Cubs.
Walker was recalled from Triple-A Sacramento on Friday and immediately made an appearance for San Francisco. The right-hander posted a 6.46 ERA and 1.89 WHIP in 15.1 innings before being optioned to Sacramento on May 10, though he was solid in his return to the big leagues. Walker threw 12 of his 16 pitches for strikes and will attempt to build on the performance in hopes of earning more high-leverage opportunities moving forward.