Mattingly has tried to rotate Yasiel Puig, Matt Kemp, Andre Ethier and Carl Crawford into the three starting spots, often citing statistical-matchup history or righty/lefty preference. Further complicating Mattingly's decisions, Scott Van Slyke has become invaluable against left-handed pitchers by hitting .444 against them.
None of the core four is on fire offensively and Mattingly said he didn't know if that was the result of irregular playing time. Puig is batting .269, Kemp .218, Crawford .217 and Ethier .206. Kemp has the highest slugging percentage at .473 and Puig the highest on-base percentage at .355.
Mattingly left Kemp out of Thursday night's lineup, even though he's 6-for-15 lifetime against Phillies right-handed starter Kyle Kendrick and had two doubles Wednesday night.
"I think Matt is disappointed," said Mattingly. "He swung the bat good last night."
Calling the lineup dilemma "a little bit of a problem," Mattingly said "there will come a day" where it will "work itself out," but he stopped short of suggesting how that might happen.
"It's not so much that you're hurting feelings," he said. "You want everybody in the mix. But you've got four guys with quality careers and you can't just throw those aside. I assume every time a name is not in the lineup, they're not happy about it."
Including Thursday night's game, Kemp had started 14 games, Puig 16, Ethier 16, Crawford 13 and Van Slyke six in the outfield.
Kemp, Ethier, Crawford and Puig are signed to long-term contracts through at least 2017. Management has been reluctant to trade any of them because Kemp and Crawford have significant histories of injury.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.