"Just some slight irritation around the ulnar nerve which created weakness," Yost said. "[Trainer] Nick [Kenney] doesn't think it's anything serious. Doesn't think he will miss his next start."
Ventura will be treated to remove the inflammation and will throw a side session on Monday in Milwaukee. If that goes well, he could make his next start on Wednesday.
Yost said the Royals' medical staff isn't sure what caused the inflammation.
"Just a freak thing and one of the things that guys that throw hard have to deal with," Yost said.
Jeffrey Flanagan is a reporter for MLB.com. Follow him on Twitter at @FlannyMLB. This story was not subject to the approval of Major League Baseball or its clubs.