Mesoraco, on the seven-day DL due to a concussion, was eligible to be activated on Wednesday, but Dioner Navarro started behind the plate in the finale with the Brewers. Navarro caught Reds starter Mat Latos in Spring Training, and was 2-for-6 with a home run against Milwaukee starter Randy Wolf entering Wednesday.
"He's had pretty good success against Wolf," Baker said.
Starter Ryan Hanigan will get three days off and catch the final two games of the Cubs series, Baker said.
"He's caught a lot," Baker said. "When he catches too much, he wears down."
Mesoraco is also appealing a three-game suspension he received for making contact with umpire Chad Fairchild on July 30 during a heated argument in the third inning of a game against the Padres.
Mesoraco was involved in a hard collision at home plate an inning earlier. He started the next night's game but left after becoming dizzy, and he was then placed on the DL.