The Cubs' game against the Reds was tied at 4 when Cincinnati had two on and two outs in the ninth against Fujikawa. The right-hander said he felt some soreness on the first pitch to Joey Votto, who drew a walk.
Athletic trainer Ed Halbur then went to the mound, and Fujikawa was removed from the game. Kevin Gregg got Brandon Phillips to fly out and end the inning, and also pitched the 10th, picking up the win.
Cubs manager Dale Sveum said Fujikawa's injury appears to be the same as what sidelined him earlier this season. The Cubs' bullpen is already short-handed with Shawn Camp on the disabled list because of a foot injury.
Fujikawa is to be examined Monday in Chicago. The Cubs will likely make a roster move Monday as well.
Fujikawa is carrying a 5.25 ERA and has allowed seven runs over 12 innings pitched in as many games this season.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.