"We are not concerned about it," manager Matt Williams said Friday. "If the season started [today], he could go. He could pitch, but we are not going to take any chances.
"We will push him [back] a couple of days and redo the pitching schedule. We'll make sure he is good next time out, that's all."
Fister made his Nationals debut on Sunday against Miami and allowed a run in two innings. After the game, he said he needed to work on his command.
"Overall, not bad," Fister said Sunday. "Obviously there are still a lot of things I need to work on. The biggest thing is my command. I felt a little erratic in there. I'm trying to get to know myself again this year. A lot of it is fine-tuning the sinker."
With Fister out Friday, right-hander Tanner Roark was scheduled to start against Houston.
Fister was acquired from the Tigers in December for infielder Steve Lombardozzi and pitchers Robbie Ray and Ian Krol.
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.