With Spring Training fast approaching, MLB.com takes a look at a different aspect of this year's Nationals squad each day this week. Today's topic: Predicting the 25-man roster.
WASHINGTON -- The Nationals' starting lineup and rotation are all but set, barring injury, yet they will enter Spring Training with a few unknowns on their Opening Day roster. Notably, the bullpen likely has at least three spots up for grabs, while the bench has one opening.
Predicting the Nats' Opening Day roster has been a difficult task in recent years, due to the strong consideration they give to non-roster invitees. Outfielder Chris Heisey and reliever Matt Belisle made the team out of Spring Training in 2016, and they stuck around for the entire season.
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Here's a first look at who will emerge from this year's group heading into Spring Training:
Catchers (2):Derek Norris and Jose Lobaton
Both Norris and Lobaton are under contract. Norris was brought in to become the starter, while Lobaton has familiarity with a pitching staff that enjoys throwing to him. This will leave Pedro Severino, the Nats' No. 11 prospect as rated by MLBPipeline.com, in the Minors to begin the season.
First base (2):Ryan Zimmerman and Clint Robinson
Zimmerman will start at first, as the Nats hope he rebounds from a disappointing 2016. However, Robinson is trying to bounce back from his own down season, too. While Robinson's roster spot should be secure since he has become one of Washington's go-to bats off the bench the past two seasons, a strong spring would help erase any doubts.

Second base (1):Daniel Murphy
Murphy, the runner-up for the National League Most Valuable Player Award, will be counted on as the everyday second baseman. But expect the Nats to give him a breather when necessary to ease the pressure on his legs.
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Third base (1):Anthony Rendon
Rendon appeared in 156 games this past season, the second most on the team. If he's healthy, he will play.
Shortstop (1):Trea Turner
Turner will return to his natural position, after spending 2016 learning center field on the fly. Washington teased using Turner as a utility player at times early in the offseason. So while he could still fill in at second base or in the outfield, expect him to get as many reps at shortstop as possible.
Utility infielder (1):Stephen Drew
Drew showcased his versatility this past season, and the Nats re-signed him to deliver more of the same in 2017. He will likely bounce around the infield for most of the season, serving as the backup at second base, shortstop and third.
Outfielders (5):Bryce Harper, Adam Eaton, Jayson Werth, Michael Taylor and Heisey.
Harper, Eaton and Werth are locked in as the starters. The final bench spot will likely come down to a battle for the fourth-outfielder job between Taylor and Brian Goodwin. Heisey has been successful in his career as a pinch-hitter and matching up against left-handers, but not so much as an everyday player. Despite his struggles at the plate, Taylor still provides some power and strong defense at all three positions.
Rotation (5):Max Scherzer, Stephen Strasburg, Tanner Roark, Joe Ross and Giovany Gonzalez
The rotation should be set, unless one of these five starters suffers an injury. It was one of the team's most consistent strengths in 2016, and it is expected to remain the same this season.

Bullpen (7):Shawn Kelley, Blake Treinen, Sammy Solis, Oliver Perez, Koda Glover, Vance Worley and Enny Romero
The first four should be locks for the Opening Day roster, with Kelley, Treinen and Solis likely to have a spring-long competition for the closer's job. Glover could also enter that battle, thanks to his rapid ascension in 2016, provided he is not experiencing any ill-effects from the labrum tear in his left hip suffered at the end of the season. Worley is a non-roster invitee who has shown some versatility as a starter, long reliever and short-inning reliever. Romero, a hard-throwing left-hander acquired this week from the Rays, could make the roster since he is out of options.
Still, the bullpen is where things can change quickly -- with pitchers like Trevor Gott, A.J. Cole and Austin Voth among those with a shot to make the Opening Day roster.