The Giants optioned right-handed pitcher Jake Dunning to Triple-A Fresno and recalled righty George Kontos, the team announced on Twitter.
Kontos, 28, is 0-2 with a 4.91 ERA and 28 strikeouts in 18.1 innings over 11 games with the Grizzlies this season.
Last season the 28-year-old, three-year veteran was 2-2 with a 4.39 ERA and 47 strikeouts over 55.1 innings with the Giants.
Dunning, 25, appeared in just one game with the Giants this year, lasting two-thirds of an inning and 13 pitches against the Pirates on Monday.
While with the Grizzlies this season, Dunning pitched 14.1 innings with a 2.51 ERA and 11 strikeouts.