Santillan has given up four earned runs on six hits and two walks while striking out seven in six innings across six relief appearances for Triple-A Louisville since the Reds optioned him to the minors July 19.
Santillan was summoned from Louisville to serve as the 27th man in the Reds' July 18 doubleheader with the Giants, but he was sent back to the minors a day later. He retains a spot on the 40-man roster and could be in the mix for a call-up later on this season.