The Giants optioned Brennan to Triple-A Sacramento on Monday.
The Giants needed space on the roster after recalling both Jesus Rodriguez and Bryce Eldridge from Triple-A, resulting in Brennan going down to the minors and Jerar Encarnacion being designated for assignment in corresponding moves. Brennan appeared in just five games for the Giants since being recalled in mid-April and went 0-for-9 with two strikeouts across those outings. He'll get more reps in Triple-A, where he is slashing .400/.396/.560 with one home run and 10 RBI in 54 plate appearances.