The Royals also announced that right-handed reliever Blake Wood will have Tommy John surgery as well, after both pitchers met with Yocum in Tempe, Ariz. The surgeries will be performed within two weeks in Los Angeles.
That makes four such surgeries for pitchers the Royals' system this year. Closer Joakim Soria, a right-hander, had the elbow reconstruction by Yocum on April 3. Left-hander John Lamb, a top Minor League prospect, underwent the surgery on June 3 and is rehabbing at Surprise, Ariz.
The Royals noted that Duffy had a tear in his ulnar collateral ligament since 2010 and that Wood had pitched with a similar condition since 2009. Minimum recovery time from the surgery typically is 12 months, but can be longer depending on the case.
"Once a player gets to the big leagues and has Tommy John, his percentage of making it back are higher than a Minor League player who has never been to the big leagues," Royals manager Ned Yost said. "They did the hard part, they got to the big league level before they had to have these surgeries, so we look for both these guys to come back as strong, or even stronger than before the injuries occurred."
Duffy came out of last Sunday's game at Chicago in the first inning and the initial diagnosis last Monday pointed to surgery. He finishes the season with a 2-2 record and 3.90 ERA in six starts.
Wood was shut down during Spring Training with what was termed a right ulnar nerve irritation. In his two seasons in the Royals' bullpen, Wood had a 6-6 record, one save and a 4.30 ERA in 106 games and 119 1/3 innings.
Soria is continuing his recovery in Arizona. He's had Tommy John surgery twice.
"He's doing great. He hasn't had any setbacks and is right on schedule with his rehab," Yost said.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.