The Cubs optioned right-handed pitcher Justin Berg to Triple-A Iowa.
Dempster was placed on the disabled list on July 7 after suffering a fracture to a toe on his right foot after he jumped over the fence in front of the Cubs' dugout to celebrate a win.
Dempster was 5-5 with a 4.09 ERA before being put on the DL.
Berg was recalled from Iowa on Saturday, but did not make an appearance. He is 4-1 with a 2.00 ERA in Iowa.
Information from The Associated Press was used in this report.