Detwiler is on the 60-day disabled list with a herniated disc in his back, his second DL stint of the season.
Johnson said Detwiler will throw one more bullpen, likely on Tuesday, before facing live hitters. If all goes well, he will be available pitch out of the bullpen.
Detwiler has told Johnson that he does not want to pitch in a winter league after the season ends. Johnson said he would leave that decision up to pitching coach Steve McCatty and general manager Mike Rizzo.
"I think the sooner [Detwiler] can come back and pitch, the more he can get up and throw and see that he's going to get by this," Johnson said.
Tom Schad is an associate reporter for MLB.com.
This story was not subject to the approval of Major League Baseball or its clubs.