There's no timetable for Sweeney's return, Cubs manager Rick Renteria said. The outfielder was 11-for-55 in 20 games before he was injured.
Sweeney had been rehabbing at the Cubs' complex in Mesa, Ariz., before he joined the Kane County team.
"We'll just continue to monitor him for the next few days," Renteria said.
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.