The Dodgers have not determined how McCarthy will be used during the final two weeks of the season.
"Obviously, the simple thought is to get him out of the bullpen, and to see how that looks," Roberts said. "But if there's a potential to get him a start, it's a possibility."
McCarthy posted a 2.87 earned-run average in his first 12 starts this season before coming undone from a combination of command issues, tendinitis in his knee and recurring blisters on his pitching hand. He has not pitched for the Dodgers since July 20.
BARNES LIKELY TO START ON SUNDAY
With Nationals ace
Barnes has outperformed Grandal at the plate this season, and has earned Roberts' confidence as a game-caller.
"Last year, my first time being around him, the game was very fast," Roberts said. "Offensively, behind the plate, communicating with pitchers. And this year, it's really, really slowed down, in all phases of the game. The way he's receiving information, the way he's communicating with pitchers and conducting himself in the batter's box, all things very positive. Very pleased."
Grandal, meanwhile, leads the sport in passed balls and was hitting .157 since Aug. 1, heading into Saturday's game.
DODGERS SET ROTATION FOR PHILADELPHIA
Maeda gave up four runs in three innings in Monday's late-night, rain-delayed mess in San Francisco.