The move came just before a key series with NL West rival San Francisco Giants, who entered play Monday night 3½ games behind the Dodgers.
Hamstring injuries have plagued the Dodgers all season. Yasiel Puig has twice been on the DL with a strained hamstring and could be out until the eve of the playoffs with a right hamstring strain. Howie Kendrick has been out since Aug. 9 with a hamstring injury, and his rehabilitation has been slowed in recent days. With Hernandez out, that means three of the Dodgers' best right-handed hitters are shelved by the same injury.
Mattingly said the Dodgers' medical staff is undergoing an internal review to "evaluate themselves and make sure they're not missing anything."
"I've been with different teams over the years, and sometimes it's the obliques," he said. "This year, for us, it's the hamstrings that have cost us."
Losing Hernandez is a bigger blow than it might appear. Hernandez, 24, is batting .361 since his playing time increased after the All-Star break. He has played six positions, most of them at an adequate level. Overall, he is batting .308 with a .492 slugging percentage.
His absence also makes it difficult for the Dodgers to spell slumping center fielder Joc Pederson, who has managed just five base hits in his last 60 at-bats. Mattingly said the team is contemplating using speedy second baseman Jose Peraza at times in center field, where he has experience in the minor leagues.
Meanwhile, the first wave of September call-ups has begun trickling into the Dodgers' clubhouse. The team recalled catcher Austin Barnes from Triple-A Oklahoma City on Monday. Reliever Joel Peralta will come off the DL, and pitchers Ian Thomas and Mike Bolsinger will be recalled Tuesday.
Mattingly said that will be it for the first wave, but he said the team hasn't ruled out promoting either of its top prospects, Julio Urias or Corey Seager, both of whom now are in Triple-A. Urias was promoted from Double-A Tulsa on Monday.