The NL East foes open a three-game series in Miami on Monday night.
After scoring 20 runs in three wins over the Chicago White Sox, Washington plated five total runs - one in the last two games - during an 0-3 weekend set with Atlanta, winner of nine straight. The Nationals hadn't been swept since Sept. 14-16 at Atlanta.
"We just got waffled today. I don't put too much stock in it," manager Davey Johnson said following a 9-0 defeat Sunday.
Washington (7-5) might be a little more concerned to open its six-game trip had it not outscored Miami 11-1 in a three-game home series April 1-4.
Jordan Zimmermann (2-0, 2.08 ERA) had a chance to help Washington become the first team in 50 years to record three straight shutouts to open the season. However, he gave up a second-inning home run to Justin Ruggiano in the 6-1 victory.
The right-hander went seven innings and gave up two runs in a 5-2 win over Chicago on Wednesday.
The Marlins (2-10) have hit one home run since Zimmermann's start against them, and they're batting .204 with a major league-low 20 runs after scoring four times in a three-game weekend set with Philadelphia.
Having slugger Giancarlo Stanton back could add some much-needed pop to Miami's lineup, but the slugger will likely miss a fourth straight game with a left shoulder bruise. There's also a chance he could end up on the disabled list.
The Marlins will also be without reserve outfielder Austin Kearns on Monday after he was taken to the hospital with an irregular heartbeat prior to a 2-1 loss Sunday. Ruggiano replaced him in right field Sunday, a day after he sat with a tight right groin.
The lack of outfield depth will likely force the Marlins to make a move before this series.
"We can't play down two or three guys for very long," first-year manager Mike Redmond told the Marlins' official website. "We hope that after today, we'll figure out where we are at."
Right now, that's at the bottom of the division as Miami is off to its worst start since opening 1-11 in 1998.
Wade LeBlanc (0-2, 3.27) has turned in two solid outings but the Marlins have scored three total runs in those games.
Facing Zimmermann on April 4, the left-hander lasted five innings and gave up three runs and five hits. Two of them were to Bryce Harper, who went 6 for 16 with two homers, a double and three RBIs in that series.
Harper leads the Nationals with five homers and 10 RBIs, but he's gone hitless in his last nine at-bats.
Nationals second baseman Danny Espinosa, 0 for 11 against the Marlins this season, is questionable after getting hit on the right wrist by a pitch and leaving Sunday's game. Steve Lombardozzi, a career .353 hitter in Miami, would likely get the start if Espinosa can't go.
Washington hasn't lost four straight since dropping its fifth in a row Aug. 28, 9-0 at Miami. The Nationals went 3-6 at Marlins Park in 2012 - their worst road record against any division opponent.