Jackson was optioned to Triple-A Sacramento on Tuesday, Maria I. Guardado of MLB.com reports.
Jackson has a 3.68 ERA, 1.09 WHIP and 21:6 K:BB over 14.2 innings for the Giants this season, but he'll now head back to the minors. The veteran right-hander is a strong bet to rejoin the big-league club at some point down the stretch.