Ross Detwiler. (Bill Boyce / AP)

Ross Detwiler will miss another month because of an issue with a disk in his back, which is pinching a nerve and causing back spasms, Manager Davey Johnson said after Wednesday’s game. The left-handed starter will not require surgery, Johnson said. The Nationals sent Detwiler to Los Angeles on Monday to receive a second opinion from well-known back surgeon Robert Watkins Sr.

“He’s got to rest it,” Johnson said.

The Nationals have been concerned with the left side of Detwiler’s lower back, which hasn’t improved since he was sidelined and placed on the disabled list July 4. Detwiler threw a bullpen session on July 19 but it was an abbreviated session because of the back discomfort.

The news, although not unexpected given the lack of improvement in Detwiler’s back, deals the Nationals a significant blow. They have patched up the back of their rotation with rookie right-handed starter Taylor Jordan, but he is about 20 to 30 innings away, according to Johnson, from reaching his innings cap in his first full season back from 2011 Tommy John surgery.

Detwiler hasn’t been the same since he returned from a strained oblique in his right side. He posted a 2.76 ERA in his first eight starts, but in five starts since his return from the disabled list because of the oblique injury, he has punched up a 6.31 ERA. The back end of the Nationals rotation, including Dan Haren and his 5.79 ERA, have been a major issue and could force the team to continue exploring adding a starting pitcher via trade.

Jordan could have about a month’s left worth of starts left, which could roughly coincide with Detwiler’s recovery. But that timetable may not factor in the time needed for Detwiler to begin throwing and pitch on a rehab assignment. The Nationals have eyed Ross Ohlendorf as a potential replacement in the rotation with Jordan’s shutdown looming and Detwiler’s lingering back injury. Ohlendorf has been terrific since joining the Nationals, posting a 2.03 ERA in 26 2/3 innings, which includes one start. The right-hander is slated to start the night game of Friday’s doubleheader.