"We're cautiously optimistic that it's going to be the same thing he had before," Cubs general manager Jed Hoyer said. "We'll find out more tomorrow."
Fujikawa will undergo an MRI on Tuesday.
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 in the Cubs' 5-4 victory.
Fujikawa has a 5.25 ERA in 12 games this season, giving up seven runs over 12 innings.
The Cubs' bullpen is already short-handed with Shawn Camp on the disabled list because of a foot injury.
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.