Zimmermann had an MRI and an X-ray to determine the severity of the injury. As things stand, manager Davey Johnson is concerned and wants Zimmermann held out of the All-Star Game.
"I'm going to recommend to [NL manager Bruce] Bochy that he miss the All-Star game," Johnson told the Associated Press. "I was concerned with him last night. I knew that it was something that was still there. Jordan mentioned it before the game to [Steve] McCatty, the pitching coach."
Johnson was reportedly unable to reach Bochy on Friday, but obviously Bochy will grant Johnson's request and replace Zimmermann on the official NL roster.
Keep in mind, replaced players can still officially count as All-Stars and attend all the festivities. They just aren't eligible to appear in the game.
Johnson told the AP that he would lobby for another Nationals pitcher to take Zimmermann's spot. Good cases can be made for Gio Gonzalez (7-3, 3.03 ERA, 114 K) and Rafael Soriano (2.13 ERA, 24 saves).
Also, keep in mind that pitchers who start on Sunday are ineligible to pitch in the All-Star Game. That means -- unless rotation plans change -- Jeff Locke of the Pirates, Travis Wood of the Cubs and Adam Wainwright of the Cardinals will also need to be replaced.
Zimmermann, 27, is 12-4 with a 2.58 ERA, 0.97 WHIP and 95 strikeouts in 132 1/3 innings pitched this season.