Dempster underwent an MRI on Friday, though the results were unclear prior to the game. As a precaution, right-hander Randy Wells was brought to Chicago from Triple-A Iowa and will take Dempster's turn in the rotation if he is unable to pitch.
"We'll probably find out more tomorrow," manager Dale Sveum said after Friday's 9-4 loss to the Reds. "We'll probably make a decision later tomorrow afternoon."
Dempster is off to a fast start, though the lack of run support has left him with an 0-1 record. He has a 1.33 ERA in three outings and has struck out a National League-high 23 batters.
Wells was a late cut in Spring Training after spending the last three seasons as a member of the Cubs' rotation. He's 27-30 with a 4.05 ERA over that span.
Wells was 1-0 for Iowa, but he had a 9.42 ERA over three outings.