According to manager Matt Williams, Zimmermann felt fine on Wednesday evening when the two had a chat in the outfield. But early Thursday morning, Zimmermann felt "sick to his stomach" and was vomiting.
"Jordan is feeling really bad. He was up all night," Williams said. "Right now we are getting some fluids in him and we'll get him back to DC, get him some rest today and re-evaluate tomorrow. We have to go day by day."
If Zimmermann can't pitch the home opener against the Braves on Friday at Nationals Park, Williams could use the bullpen that day, which means Ross Detwiler and Craig Stammen could see action. However, Detwiler pitched two innings against the Mets on Thursday, and Willliams indicated that Zimmermann could pitch the opener, but they will not know until Friday morning.
"We still don't know. We still don't know how he is going to feel when he gets to the ballpark in the morning," Williams said.
Right-hander Taylor Jordan is not an option to pitch Friday because he pitched a simulated game Tuesday. He is scheduled to pitch his first game of the season on Sunday against the Braves.
"If [Zimmermann] is not ready to go, [the bullpen] would be our option," Williams said.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.