"It's similar to the post-surgery muscle spasms I have had in the past," Johnson said. "There's no involvement down the legs, which is the first thing they ask you. There's no nerve issue, which is good for me. In the past, it didn't take the full 15 days. I'd play a few [rehab] games and be back on the field the day I can come off.
"We're in a situation where we all knew I didn't need the full 15 days, but I had a head start missing six days, and with the All-Star break it made sense rather than go out there with lingering pain that gets worse."
Johnson spent stints on the disabled list in 2008 and 2009 with a similar problem. This time, he said, he first felt it in a game against the Yankees advancing to third base on a Clayton Kershaw bunt and it worsened while making a quick turn in a game against the Cubs last week.
He said he would like to play in a couple Minor League rehab games next week in the California League before being activated. He is eligible to return a week from Saturday, but is not scheduled to resume baseball activities until this weekend.
"My back always has done better when I'm on the field more," he said. "I get into a situation when I don't play for five or six days, then I play for one or two and that's probably tougher on my body. I need to recognize that and make sure I get simulated activity, like sprinting with my spikes on."