The Royals placed Kennedy on the 10-day DL with a left oblique strain Wednesday, one day after the right-hander pitched just three innings against the Minnesota Twins.
Kennedy was making his return from the DL after being sidelined since late June, also because of a left oblique strain. He said that the new injury was in a different location than his previous oblique strain.
"All week, the last 10 days, everything has been getting better,'' Kennedy said Tuesday after the Royals' 9-4 victory. "It felt great all night, and then all of a sudden I felt something at the bottom of my ribs. ... It's just aggravating."
Kennedy, 33, has struggled this season, going 1-8 with a 5.13 ERA. The 12-year veteran is in the third year of a five-year, $70 million contract with the Royals.
The Royals recalled right-hander Jason Adam from Triple-A Omaha to replace Kennedy on their 25-man roster.