Peralta, on a rehab assignment with Double-A Springfield, had to get three stitches and will not play for three or four days, manager Mike Matheny said.
Peralta cut himself while using a knife on his birthday, an eerily similar injury to the one Matheny sustained when he was a Cardinals catcher in 2000. Matheny sliced his thumb on his birthday while examining a hunting knife he had received as a gift and had to have surgery to repair a tendon.
"I just don't have any idea how someone could cut their hand. That just amazes me," Matheny joked. "I feel for him because I've been there. Fortunately, his isn't that big a deal, just a minor setback. We can't bubble-wrap guys. You have to live life, and there are going to be things that happen."
Peralta might resume his rehab assignment up a level with Triple-A Memphis, Matheny said. But the Cardinals now have ruled out his returning to the majors as soon as Friday, because he needs more minor-league at-bats. Peralta tore a left thumb ligament near the start of spring training and had surgery a few days later.
Peralta has batted .200 with a double and two strikeouts in 15 at-bats on his rehab assignment thus far. He has played both shortstop and third base and might be asked to play multiple positions when he returns to the Cardinals. Rookie shortstop Aledmys Diaz is batting .319 this season for St. Louis.