The Red Sox placed Mayer on the 10-day injured list Friday with a stress reaction in his left forearm, Mac Cerullo of the Boston Herald reports.
Interim manager Chad Tracy said that Mayer's injury is something that he's been dealing with for a while, so the team will place him on the IL to allow him to heal properly. Tsung-Che Cheng will come up from Triple-A Worcester to fill the open roster spot and is likely to receive a handful of starts while Boston also navigates injuries to Isiah Kiner-Falefa (forearm) and Nick Sogard (oblique).