The Giants optioned Black to Triple-A Sacramento on Friday, Maria I. Guardado of MLB.com reports.
Black was saddled with his fifth loss of the season Wednesday versus Arizona, allowing four earned runs on five hits and five walks across just 2.2 innings. Now that his spot in the rotation won't be needed for the rest of the season, the Giants will send him back to the minors and insert Randy Rodriguez (elbow) back into their bullpen.