Jordan Zimmermann. (Photo by Jonathan Newton / The Washington Post)

Tanner Roark wasn’t told until early Thursday morning that he would be starting a day earlier than expected. The right-hander was scheduled to make his first start of the season in Friday’s home opener in Washington but the plan changed after Jordan Zimmermann, originally scheduled to start, was up all night, vomiting and running a fever. Pitching coach Steve McCatty delivered the news to Roark.

Williams said Zimmerman appeared well on Wednesday. He came to Citi Field on Thursday morning and received fluids, but was then sent back to Washington ahead of the team so that he could rest. If he hasn’t improved by Friday morning, the Nationals could use a combination of relievers to eat up the innings instead. Left-handed reliever Ross Detwiler, a former starter, would be the logical choice to start the game. Craig Stammen is another possibility.

“We’ll see how it goes,” Williams said. “Get him some good fluids today, get him back home and get him rested up. But he’s feeling bad.”

Detwiler hasn’t pitched in a game since March 26, the penultimate spring training game, and he was scheduled as a must-pitch in relief on Thursday. But now, Detwiler could potentially be held out of Thursday’s game as insurance for Zimmermann if he isn’t ready for Friday’s start. That’s hard news for a rookie manager to deliver to a pitcher who moved out of the starting rotation and into the bullpen during spring training.

For the rest of the Braves series, the Nationals will send Stephen Strasburg to the mound in Saturday’s game and Taylor Jordan on Sunday. Jordan is not available until then because he threw a simulated game on Tuesday. His Sunday start would be on the usual five days’ rest. Now Roark has been thrust into an unenviable position of preparing to face one team, the Braves, and now facing another, the Mets.

“It’s never comfortable for anybody, because they hadn’t planned on it,” Williams said. “All of a sudden, they wake up in the morning, and there’s a phone call. Hey, you’re starting today instead of [Friday]. Our guys are ready to go. They’re ready to play at any given time. Tanner is no exception. He’s ready to go out there.”

Flu and chest colds have been going around the Nationals clubhouse all spring and early this season, and has affected, among others, Bryce Harper, Anthony Rendon, Rafael Soriano, Tyler Moore, Jeff Kobernus and now Zimmermann. “We’ve had a lot of that this spring, guys feeling sick,” Williams said.

Roark made a splash last season when he was called up in the summer as a bullpen reinforcement and then made starts down the stretch. He went 7-1 with a 1.51 ERA over 53 2/3 innings. He impressed the Nationals with his command, poise and stuff, a sinker and curveball which are underrated.

“He doesn’t blow up the radar gun, but he doesn’t have to,” Williams said. “He changes speeds and he throws strikes. He’s good. Good pitcher.”