Hammel, 5-4 with a 2.86 ERA in 17 starts, left Wednesday's game against St. Louis because of tightness in his left hamstring. An MRI showed no major structural damage, and manager Joe Maddon has the right-hander penciled in to start at Cincinnati on July 21.
Maddon says that's "what it looks like right now" and the Cubs will "see how it all plays out." He spoke before Friday's game against the crosstown White Sox.
The Cubs reinstated Mike Olt, sidelined by a hairline fracture in his right wrist, from the 60-day disabled list and optioned him to Triple-A Iowa. They also designated right-hander Donn Roach for assignment.