Still experiencing the same lower back discomfort that nearly sidelined him a week ago, Ross Detwiler will have to make another trip to the disabled list.

Manager Davey Johnson said Detwiler didn't appear to be 100 percent healthy during his between-starts bullpen session earlier today. The left-hander was due to take the mound Monday in Philadelphia, but Johnson said the club doesn't want to take a chance and will place him on the DL.

"He's a tough customer," Johnson said. "But he understood the value of getting by this thing. He got a whole lot of treatment today, and so hopefully we can get by. He'll be good coming back after the [All-Star] break."

Detwiler already missed a month earlier this season with a strained oblique muscle. This back issue is unrelated, but it first cropped up during his June 28 start in New York.

Detwiler is receiving treatment and was scheduled to be examined by team orthopedist Wiemi Douoguih on Sunday, but the Nationals already appeared to prefer a cautious route with the pitcher, especially with the All-Star break approaching. The club could use those four days off to help buy Detwiler some more time and let him rest until their need a fifth starter coming out of the break: July 23.