Duffy was diagnosed with a torn ulnar collateral ligament in his left elbow following his early exit from Sunday's game against the White Sox in Chicago.
Duffy said that he felt a "snag" in his elbow after the game's second pitch. He threw 11 more before leaving in the first inning. Royals catcher Humberto Quintero visited the mound, and Duffy said Quintero told him, "I'm not going to let you pitch like this."
"Second pitch, I tried to go up and in on him, and that's when I felt it, on extension," Duffy explained. "Every pitch after that was just kind of hectic for me. I can't thank Quintero enough for coming out and getting me after that. He's definitely a seasoned vet. He knows the game well. It could have been a lot worse had it not been for him."
Duffy will see Dr. Lewis Yocum in Tempe, Ariz., on Friday to get a second opinion, but he is resigned to the fact he'll be having Tommy John surgery.
It's a procedure that teammate Bruce Chen has gone through and returned from. Teammate Joakim Soria is currently recovering from the surgery, which was performed by Yocum. Duffy said he looks at all the pitchers who have come back from the procedure and it gives him confidence.
"I'm very positive going in," Duffy said. "They've got it down to a science now. I feel very lucky that this happened in this period of time as opposed to 20 years ago.
"Dr. Yocum, or whoever it's going to be, they're all great at it, and that's why people come back stronger. Just look at [Nationals starter Stephen] Strasburg. I could name a bunch of people, so I'm not going to get too down on myself, obviously."
Duffy compiled a 2-2 record with a 3.90 ERA in six starts before the injury. He only made it more than five innings in three of those starts, though.
This isn't Duffy's first brush with elbow trouble. During Spring Training in 2010, the Royals shut Duffy down because of stiffness in his left elbow, predicting he'd be out until May. Personal reasons kept Duffy away from the organization until June, but he returned and started 17 games for four different teams in the Royals' system.
"We've known since February of 2010 that this ligament was compromised," said Royals general manager Dayton Moore. "[Head athletic trainer] Nick Kenney and our medical team, along with Danny, have done a tremendous job getting him to this stage and keeping him going the best they could. But we've known. Whenever he failed and couldn't go out there and pitch, it was probably going to be time to be a little more proactive and getting a surgical procedure. That's probably where we are at this point."
Duffy said his goal is to return to the team in June of next season. It's been said that pitchers who have the surgery often come back better than they were before, something Chen has said applies to himself. Moore's not sure about that, but he wants Duffy to return to the level he's shown the Royals he can pitch.
"The one thing about Danny, especially in the Major Leagues, you've got to be able to command your fastball," Moore said. "And often times when your arm's hurting or something's just not right, the command's really the first thing to go. Danny kept his velocity really throughout this whole issue he had with his elbow, again dating back to 2010.
"We'll see. I don't necessarily prescribe to the theory that they come back better, but that being said, if he comes back to an accustomed level, that's pretty good."
Just because Duffy won't be on the mound doesn't mean he's not going to be involved with the team. He sent tweet after tweet during the Royals' 7-4 win over the Texas Rangers on Tuesday, cheering on his teammates via social media and interacting with fans. When asked if the tweets will keep on coming, Duffy had two words: