Posey was put on the list last week after he was struck in the helmet by a 94 mph fastball from the Arizona Diamondbacks' Taijuan Walker. Posey got up on his own after being struck but exited the game, and the Giants decided not to take any chances with the 2012 National League MVP and 2010 NL Rookie of the Year.
They still weren't taking chances on Tuesday, waiting until batting practice to activate Posey and designate backup catcher Tim Federowicz for assignment.
Posey was the designated hitter batting cleanup for the opener of a two-game series in Kansas City. San Francisco bench coach Ron Wotus said Posey will likely serve as the DH on Wednesday, as well.
Information from The Associated Press was used in this report.