Royals manager Ned Yost said Monday that an MRI didn't show any structural damage. Duffy left his start Saturday at the New York Yankees after one pitch.
''He's in Kansas City going through three or four rounds of treatment every day,'' Yost said before the Royals played Detroit. ''We'll evaluate him when we get back.''
The 25-year-old is 8-11 with a 2.42 ERA.