It is the third time in four games that Zimmerman, 32, has not been in the starting lineup.
The starting first baseman on Sunday for the Nationals was Adam Lind, one of the best pinch hitters in the National League and the owner of a .333 batting average overall. Lind also started Saturday and hit a two-run homer.
Zimmerman, a University of Virginia product, entered Sunday leading the majors with a .365 average and was tied for third with 17 homers and was second in slugging at .697.
A right-handed hitter and former third baseman, Zimmerman has been dealing with back issues since he dove for a ball on Tuesday in Los Angeles in a win against the Los Angeles Dodgers.
"It's one of those things where if you continue to play and it gets worse, something bad could happen," Zimmerman said Saturday. "If you give it a day or two you can kind of just stop it right there. That's sort of the plan since it's June and we have the ability to do that. We'll see how it feels in the morning. Kind of go from there as far as tomorrow. Even if I don't play tomorrow, I can't see me not playing on Monday."
Zimmerman did not play more than 115 games the previous three seasons and was limited to 101 games in 2011 as injuries have plagued him most of the past five years. He hit a career-high 33 homers in 2009.