The Reds designated Diehl for assignment Monday.
He'll end up losing his spot on both the Reds' 40-man roster and 26-man active roster with Cincinnati needing an opening on the latter for Luis Castillo (shoulder), who was reinstated from the 10-day injured list in advance of his start Monday against the Brewers. During his nearly two-week stint with the big club, Diehl appeared in five games out of the bullpen and gave up seven earned runs on eight hits and three walks over 5.2 innings.