Duffy believes he is ahead of schedule in his recovery.
"We're flying right now," Duffy said. "I definitely feel like I could get going quicker on this. I don't want to put the carriage before the horse, but I feel like I'm ready to get going. I don't feel any pain. "If they asked me to go today, I'd go on a rehab assignment."
Duffy will throw another side session on Friday. After that, manager Ned Yost said it is possible that Duffy could go out on a rehab assignment.
"We'll just see how he feels next time out," Yost said.
Duffy said he was very pleased with his session Tuesday.
"I probably mixed in seven or eight outs with the hitters," Duffy said. "I threw everything, did my slide-step and everything. I would like to think that [a rehab assignment] would be the next course of action. If I had to put a finger on it, I'd say I'm ready to go."
In the meantime, Duffy is enjoying watching his teammates help the Royals climb the standings. Kansas City entered Tuesday's game 3 1/2 games out of first place in the American League Central.
"They're doing it, man," Duffy said. "I just want to get back and continue that and help out however I can."
• Right-hander Nate Karns, on the disabled list with forearm soreness, had been shut down for about 10 days but will resume throwing on Wednesday.
Karns was re-examined by physicians last week after experiencing lingering soreness, but Karns said his exam checked out OK.
"They just said it was taking a little longer to move out of [the forearm]," Karns said. "So we have rested and now I should be back on track."