McGehee, who did not start the Giants' 5-4 win over the Phillies, struck out as a pinch hitter in the eighth inning.
McGehee, the 2014 National League comeback player of the year in Miami, got off to a disappointing start with the Giants after signing as a free agent in the offseason. He hit .200 with a .536 OPS in the team's first 35 games this season. San Francisco sent him to Triple-A Sacramento to work on his swing, and McGehee hit .357 (15-for-42) in 10 games in the Pacific Coast League.
Matt Duffy continues to log the bulk of the time at third base for the defending World Series champions, but manager Bruce Bochy said he'll probably give McGehee a start during San Francisco's three-game series in Philadelphia this weekend.
"Casey admitted it was probably one of the best things he could have done -- gone down and gotten some at-bats," Bochy said. "It allows you to find your swing in a more relaxed atmosphere, without the added pressure. He should be in a better place."
The Giants, who ended a five-game losing streak, were without two outfield regulars for Friday's series opener at Citizens Bank Park. Nori Aoki sat out with the flu, and Hunter Pence is day-to-day with tendinitis in his left wrist.