"[The doctors] have done a lot of tests. I think they want to get another opinion because they are not sure exactly what's reoccurring," Johnson said.
Detwiler first sustained tightness in his lower back May 15 against the Dodgers. The last time Detwiler had a bullpen session was three days ago and he couldn't do a lot of running.
Detwiler has been on the DL twice this season because of the back issues. With Detwiler expected to be out, the Nationals have to decide who could be their fifth starter. Taylor Jordan, who's in the rotation, is on an innings limit this year because of Tommy John surgery he had in September 2011.
Johnson would consider giving Ross Ohlendorf more starts. The veteran righty has been successful as a long man and will start against the Mets on Friday.
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. Tom Schad is an associate reporter for MLB.com. Follow him on Twitter @Tom_Schad. This story was not subject to the approval of Major League Baseball or its clubs.