KANSAS CITY, Mo. — Royals pitcher Danny Duffy underwent surgery Tuesday to remove loose debris in his pitching elbow, and the left-hander is expected to resume his normal off-season training in about six weeks.

The Royals said that Duffy should be ready for spring training in February.

Duffy has been dealing with minor pain in his elbow for a couple years, but loose cartilage and bone chips had begun to cause inflammation. He landed on the disabled list in late August but returned to make three starts down the stretch in September.

Duffy wound up 9-10 with a 3.81 ERA over 24 starts in the first season of a five-year, $65 million extension he signed before the season. He struck out 130 while issuing just 41 walks, and is expected to be the ace of a rebuilt starting rotation next season.

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