Cubs manager Rick Renteria said Tuesday he has yet to talk to Jackson since his last Cactus League start on Friday, when the right-hander decided to only throw fastballs but didn't tell either the manager or pitching coach Chris Bosio. Jackson gave up three runs on four hits over three innings against Cleveland.
"I'm sure we'll have the discussion, and that will be between me and him," Renteria said.
McDonald, bothered last season by shoulder issues, was scheduled to go three innings on Wednesday against the Mariners.
Looking ahead, Jeff Samardzija and Travis Wood are expected to start Saturday and Sunday in split-squad games against the Royals and Indians, respectively, while Carlos Pimentel and Chris Rusin will get the assignments over the weekend in Las Vegas against the Mets.
Rusin, a candidate for the Cubs' fifth spot in the rotation, threw three hitless innings on Monday against the Giants. The lefty was so efficient that he needed to finish his work in the bullpen.
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.