Duffy, 23 , left Sunday's game in Chicago after just 13 pitches with what manager Ned Yost told reporters was elbow soreness, but it was the same type of injury that caused him to miss a start last month. He also had elbow problems last season.
Duffy was 2-2 with a 3.90 ERA in six starts this season. Last year he was 4-8 with a 5.64 ERA.
The Royals just put another left-handed starter, Jonathan Sanchez, on the disabled list last week. Sanchez had tendinitis in his left biceps. The Royals have yet to announce a replacement for him in the rotation with his spot coming up Tuesday against the Rangers.
Kansas City called up right-hander Nate Adcock from Triple-A Omaha and also have right-hnader Vin Mazzaro as a possibility.
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