But Duffy, who had Tommy John surgery in 2012, said his elbow ligament is fine.
"[The pain] is not ever going to go away until we take care of it," Duffy said. "I just have to push through to the end of the season. I've always had a pretty high pain tolerance. I'd like to say it would go away, but it won't until we address it.
"I'll just get the treatment, and continue to try and keep the pain down to nothing. It's something that is inflaming something in there. Until then, we'll just go. Nothing in my elbow is going to compromise my ligament ... it's not something major."
Royals manager Ned Yost said if Duffy is activated, he likely would be on a 60-pitch limit this weekend.
"I'm just really anxious to get back and help this team down the stretch," Duffy said. "I've never been more ready to get back on the field."
And once the season ends?
"We have a plan for the offseason," Duffy said. "I'm not going to dwell on it. Until then this is not going to mess up my ligament. That's No. 1."
Skoglund possible starter
Yost also confirmed that right-hander Ian Kennedy would indeed miss his scheduled start on Wednesday because of shoulder fatigue. Yost said the Royals would simply skip Kennedy's spot in the rotation, rather than just push him back a day or two.
"He can use the rest," Yost said.
Left-hander Eric Skoglund (1-2, 10.29 ERA) is the likely choice to start on Wednesday, if he is not needed Monday or Tuesday in long relief.
Jeffrey Flanagan has covered the Royals since 1991, and for MLB.com since 2015. Follow him on Twitter @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.