If Sandoval plays against the Arizona Diamondbacks, it would be his first appearance with the Giants since helping them win Game 7 of the 2014 World Series.
That offseason, Sandoval elected to sign with the Boston Red Sox. The three-year, $95 million contract was largely a bust, and he was released last month.
Sandoval signed a minor league contract with the Giants on July 22 and was apologetic about the way he left San Francisco three years ago.
A roster spot for Sandoval's elevation to the majors opened as the Giants placed Brandon Belt on the seven-day concussion disabled list. Belt, who has three previous concussions during the past eight years, was hit in the head by a 78 mph curveball Friday night.