The Diamondbacks optioned Bratt to Triple-A Reno on Monday, Steve Gilbert of MLB.com reports.
Bratt lasted only three innings in each of his last two starts, and he has an uninspiring 28:25 K:BB over 39.2 innings covering nine starts in the majors. The Diamondbacks have not announced who will take the left-hander's spot in the rotation later this week.