Johnson has been out since July 9 with back spasms that he's dealt with sporadically since 2007 disk surgery. He thought he was close to a rehab assignment a week ago, but suffered a setback when he ran on a treadmill.
"Today I felt good after also throwing yesterday and that was a good sign," said Johnson, whose injury, combined with Manny Ramirez's injury, led to the Wednesday acquisition of Scott Podsednik from Kansas City.
"The way it progressed from yesterday, I don't think it will be too long [before he's ready for games]. Once the spasms settled down, it usually goes fast. I just don't want to come back with it lingering. I want to come back with it completely resolved."