"We were hoping this was going to be a simple ankle sprain, but it's a lot more serious than that," said Mattingly to reporters on Wednesday. "He's been able to do some things, but is having soreness with that. We're still not where we need to be."
GM Ned Colletti added the team won't have their full complement of outfielders until "a few weeks from the end [of the season]."
Kemp, 28, has appeared in only 63 games this year due to hamstring and shoulder injuries in addition to the ankle. He had offseason surgery on his left shoulder as well. Kemp has hit .263/.319/.382 (98 OPS+) with five home runs and nine steals this season.
Even without Kemp, the Dodgers still have Andre Ethier, Carl Crawford and Yasiel Puig in the outfield. They came into Wednesday atop the NL West at 57-48.