He said Van Slyke "will play against lefties somewhere, however that works out," because Van Slyke can take over for left-handed hitters Crawford in left or Adrian Gonzalez at first base.
Ethier, at this point, isn't even in a platoon.
"He'll play all over because he can play all three [outfield spots]," Mattingly said. "He's been good coming off the bench. He'll be playing a lot."
Mattingly said he's not concerned that unhappiness over playing time will get in the way of team goals.
"It hasn't been a problem," he said.
Although Kemp never wanted to be taken out of center field, Mattingly said when they talked, Kemp "preferred right to left. It looks like he's really comfortable. I don't think it's going to be a problem at this point. We have too much on the line."
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.