Manager Bruce Bochy had said before the announced roster move that Sandoval would be activated to play in the game but would not be in the starting lineup, and that he expects Sandoval to be back in the lineup for the next two games against the Nationals.
Sandoval appeared as a pinch-hitter in the ninth inning of Monday's 14-2 loss, fouling out while batting right-handed.
"I wasn't going to start him all three games," Bochy said. "He says he feels great. The day off will be good. He should be 100 percent at that point."
Sandoval finished a three-game rehab assignment with Class A San Jose over the weekend, though he did not get any in-game ground balls while starting at third base.
After straining his left hamstring on July 24 while playing first base against the Padres, Sandoval said he still isn't running at full speed.
"I don't want to push it right now," Sandoval said. "But every day, I feel better and better."
Bochy said that Sandoval will initially strictly see time at third base, but did not rule out playing him at first base down the line.
"We're looking for him to be the guy he has been all year and drive in some runs," Bochy said.