Samardzija was slated to start Saturday's contest against the Nationals. Chicago filled that hole by starting right-hander Carlos Villanueva, who's spent the last two months pitching out of the bullpen.
The Cubs' Sunday and Monday starters will stay the same as scheduled with Jake Arrieta capping off the weekend and Edwin Jackson facing the Reds in the series opener. The team will pick up a reliever on Sunday to fill out its 25-man roster.
For Tuesday, Cubs manager Rick Renteria said Triple-A Iowa left-hander Tsuyoshi Wada will start one game of the day-night doubleheader in Cincinnati as the 26th man. Travis Wood will start the other game, but Renteria said which pitcher would start which game is still being determined.
As far as Wednesday and Thursday, Renteria said he couldn't elaborate on who's in contention to start. Hammel would have been scheduled to go on Wednesday.
"We're still in conversations to see what direction to go in," Renteria said.
Renteria said Wada remaining in the rotation to fill one of the gaps left by the departure of Hammel and Samardzija is a possibility, but decisions have yet to be made about how the Cubs want to progress as far as their starting rotation for the remainder of the 2014 season.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. Daniel Popper is an associate reporter for MLB.com. He also can be found on Twitter @danielrpopper. This story was not subject to the approval of Major League Baseball or its clubs.