The Giants activated Mayer (forearm/foot) from the 10-day injured list Monday, Alex Pavlovic of NBC Sports Bay Area reports.
Mayer has not played in the majors since late June, when he suffered a left forearm stress reaction while still in the Red Sox organization. He was also forced to slow his rehab due to a bone bruise in his right foot, but the infielder seems to have put both injuries in the rear-view mirror and will make his Giants debut at designated hitter Monday. Mayer has slashed .223/.278/.346 in 114 contests thus far at the big-league level.