"It's going to be a broader MRI than this narrow one," general manager Mike Rizzo said after the team's 6-2 victory over the Padres.
Johnson is not sure if Detwiler will make his next scheduled start against the Giants on Monday. Johnson didn't rule out having a bullpen by committee throw that day. Relievers Zach Duke or Craig Stammen could start the game. It would make sense if Stammen received the start because he pitched Wednesday, the same day that Detwiler pitched. If Detwiler misses one start, there isn't a need to put him on the disabled list.
"We think he is going to be all right," Johnson said. "He was a little stiff and sore this morning, but he is going to be all right."
Detwiler sustained tightness in his lower back in the top the third inning on a sacrifice bunt that advanced Roger Bernadina to second base. Detwiler had problems running the bases. His back got worse in the bottom of the inning.
It was believed that he hurt his back while catching a wide throw from shortstop Ian Desmond in the bottom of the third, but Detwiler said he felt fine.
Detwiler had problems throwing pitches after that, and pitching coach Steve McCatty, head athletic trainer Lee Kuntz and Johnson came to his aid. Detwiler stayed in and allowed a single to A.J. Ellis and walked Andre Ethier to load the bases. He got out of the inning when Scott Van Slyke lined out to third baseman Ryan Zimmerman. The left-hander was then replaced by Stammen
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.