The Giants optioned Jefferies to Triple-A Sacramento on Thursday, Andrew Baggarly of The Athletic reports.
Jefferies was used in bulk relief in Wednesday's 6-2 loss to the Red Sox, allowing four runs over 2.2 innings as he took the loss. He'll rejoin Sacramento's rotation, and his spot on the Giants' 26-man active roster spot will go to right-hander Randy Rodriguez, who was called up from Triple-A.