Zimmerman was shelved for the first time in his career Tuesday, getting a spot on the 15-day DL because of a shoulder injury. The Nationals now have five members of the Opening Day starting lineup on the DL.
"I'm upset. I'm frustrated," Zimmerman said. "It's tough for me not to be able to play."
Zimmerman was one of only three big leaguers to start all 162 games last season. He recently ended a streak of 205 consecutive games played.
But his shoulder hasn't been the same since a headfirst slide into second base at Baltimore on May 18. He played with discomfort for a week, then missed the last seven games. An MRI on Monday revealed a small tear in his left, non-throwing shoulder.
The DL move is retroactive to May 26.
"I like to believe I have a pretty good threshold for playing with pain, but this was just a little different," Zimmerman said. "I want to play here for a long time, and there's no reason to go out and do something to make it worse."
Zimmerman's MRI results were sent to three orthopedic specialists for additional evaluations. Two of the specialists responded last Tuesday; they recommended rest and anti-inflammatory medications and a re-examination of the injury in one week, the same treatment suggested by the team's own physician.
Zimmerman is batting .257 and leads the Nationals in both homers (8) and RBIs (27).
The Nationals this season have made 15 DL moves involving 12 players. The team had lost 323 man-games due to players on the DL entering Tuesday night's game against the St. Louis Cardinals.
"I can't control it," manager Manny Acta said. "Nobody wanted to get hurt here. Nobody's going to come in here feeling sorry for me or my team."
To take Zimmerman's spot on the roster, the Nationals recalled Kory Casto from Triple-A Columbus. Casto played in 16 games with Washington last season.
Casto started in right field Tuesday night but will also get starts at third, Acta said.
Also Tuesday, right-handed pitcher Ryan Wagner, who is on the 60-day DL, rejoined the team after a stint at extended spring training. Wagner is recovering from major shoulder surgery 12 months ago and will throw a simulated game Thursday before possibly getting a rehab assignment.