Right-handed reliever J.J. Hoover was recalled from Louisville to take Mesoraco's place on the roster.
A hyped prospect entering the season, Mesoraco struggled at the plate, batting .210 with five home runs and 14 RBIs. He was the backup behind Ryan Hanigan and primarily caught pitchers Mike Leake and Homer Bailey.
"It's a tough position, like I said in Spring Training, when you have a rookie catcher that's not playing every day and the fact that Hanigan was playing so well," Reds manager Dusty Baker said.
By going down to Triple-A, Mesoraco will have the chance to get regular at-bats as Louisville finishes the final two weeks of its season. Mesoraco served his two-game suspension on Tuesday and Wednesday for contacting an umpire during a game on July 30.
Dioner Navarro was called up to replace Mesoraco during the suspension and will remain as Hanigan's backup.
Mesoraco, 24, can still be eligible for the postseason roster despite going down this late in August. Baker felt he could still make the team in October.
"We're hoping that's what the final outcome is," Baker said. "It depends on him and depends on the progress that he makes. We really want to stress that it has nothing to do with his suspension. This has kind of been dabbled about for a while. We could see his confidence has gone down some. We want to get his confidence back, offensively, defensively, throwing and all kind of ways."