Danny Duffy is dealing with inflammation, but the shoulder itself is "structurally sound," according to the Kansas City Royals.

Duffy threw one pitch against the New York Yankees on Saturday before leaving because of left shoulder soreness.

"He has rotator cuff inflammation and will require three, four days' rest before being re-evaluated," Dayton Moore said. "He will not make his next start."

Duffy's 2.42 ERA is third best in the American League behind Chicago's Chris Sale and Seattle's Felix Hernandez.