Santillan cleared waivers Friday and was sent outright to Triple-A Louisville, Charlie Goldsmith of The Cincinnati Enquirer reports.
Santillan gave up one run over 3.1 innings in three appearances with the Reds, but a 9.26 ERA and 2.12 WHIP in Triple-A was enough to discourage interest from other teams. He will almost certainly remain in Louisville to finish the season.