Duckworth rejoined the Royals from Omaha on Aug. 24 and made seven starts. He had a 3-3 record and a 4.50 ERA, finishing strong with three straight quality starts. He will be invited to Spring Training with the Major League club.
His assignment to Omaha leaves the Royals with 38 players on the 40-man roster.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.