The Royals released Duffey on Tuesday, Robert Murray of FanSided.com reports.
The right-hander has been at Triple-A Omaha since being designated for assignment in late May, and he's now been released. Duffey allowed five runs with a 10:8 K:BB over nine innings with the Royals and pitched to a 2.35 ERA, 1.16 WHIP and 34:11 K:BB in 23 outings for Omaha.