The Reds designated Detwiler for assignment Tuesday.
Detwiler's removal from the 40-man roster comes after he allowed five earned runs and eight baserunners in 2.1 innings over his last two relief appearances, inflating his season ERA and WHIP to 4.44 and 1.56, respectively. The Reds selected reliever Derek Law's contract from Triple-A Louisville to fill Detwiler's spot on the roster and in the Cincinnati bullpen.