"We're going to have to get down the road a bit and see where he's at," Yost said of Kennedy. "I'm not incredibly optimistic that he's going to make it."
Yost's options to make that start?
"Not ready to talk options yet," Yost said.
The good news is that Yost expects Soria, recovering from an oblique strain, to return on Monday. Soria would be mixed in with the rest of the closer-by-committee relievers taking over for Kelvin Herrera, who was demoted from the closer's role on Friday.
"We'll have to get Jack's feet on the ground first, of course," Yost said.
Duffy, recovering from left elbow impingement, is scheduled to throw a two-inning simulated game on Monday. If all goes well, Duffy could be activated for next weekend's series against the Indians at Progressive Field.
Yost also said that once Duffy is back and the Royals reach their final scheduled off-day on Sept. 18, the club may finish out the regular season with a six-man rotation.
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.