Third baseman Ryan Zimmerman will be placed on the 15-day disabled list with a strained abdominal muscle, according to a team source. Zimmerman first dealt with the injury during spring training and severely aggravated it Saturday night against the New York Mets.

Zimmerman sat out Sunday’s game, meaning the soonest he could return is April 24. But Zimmerman will miss more time than that. The Nationals hope he will return in three weeks, but it could be longer. Until then, the Nationals will be without their best player and No. 3 hitter. Zimmerman, 26, also missed the final two weeks of last season with a strained oblique, an injury not related to this.

Zimmerman hurt himself when he slid into second base, taking an extra base on a single when the outfielder’s throw went to third. It was an especially unfortunate injury, since the ball never went to second base, making the slide unnecessary. Zimmerman actually stayed in the game and went 1 for 3 with a single.

This will be the third time in four years Zimmerman has been sidelined for a significant chunk of time by an injury. Although Zimmerman did not land on the disabled last year, he played 142 games last season, missing time at the end of the season with an oblique injury and also sitting out a smattering of games early in the year with two separate hamstring strains. Zimmerman played only 108 games in 2008 after he hurt his left shoulder, also when sliding headfirst. In 2007 he played in all 162 games, and he played 157 games in both 2006 and 2009.

It is not yet known who will take Zimmerman’s spot on the 25-man roster. The leading candidates are likely utility infielder Brian Bixler and outfielder Roger Bernadina, both currently at Class AAA Syracuse. Bernadina had missed the first four days of Syracuse’s season attending to a family matter, but he was scheduled to return to the team last night.

Starting Tuesday in a series-opener against the Phillies, the Nationals will have to adjust their lineup without Zimmerman. Jerry Hairston and Alex Cora will likely split time replacing him at third base. Jayson Werth, who has hit second every game Zimmerman has been in the lineup, will likely slide down to third. Rick Ankiel, Danny Espinosa and Hairston are all candidates to hit second in Werth’s place. Zimmerman was hitting .357 with a .486 on-base percentage and a .536 slugging percentage.