Christian injured his wrist in Wednesday's 8-4 win against the Dodgers after joining the Giants from Fresno following Melky Cabrera's suspension.
"The good news there is nothing is broken or damaged, but he's going to be out four to five days," manager Bruce Bochy said.
Peguero, who has yet to play in a Major League game, was expected to join the team around an hour before the start of Thursday's game. The 25-year-old Peguero joins the Giants after hitting .272 for Fresno and had a 22-game hitting streak end Wednesday.
"He's a strong kid and he's a good outfielder with a good arm; he runs well," said Bochy, who has seen Peguero play during several of the past Spring Trainings. "He's been swinging the bat well. This is an easy one for us."