"A decision was made because, even prior to playing catch, I had some symptoms in my leg," Johnson said on Tuesday. "The plan is to miss today's start, take about another 10 days off and reevaluate where I'm at at that time and set a game plan 10 days from now.
"I'll let it calm down a little bit over the next 10 days. Hopefully everything will get a little bit better and we'll go from there."
Johnson was put on the DL on Tuesday, and 22-year-old right-hander Yusmeiro Petit was recalled from Triple-A Tucson to make the start on Tuesday night in St. Louis. Petit flew from Sacramento on Tuesday morning and arrived at Busch Stadium a little more than three hours before first pitch.
"We will DL him," D-backs manager Bob Melvin said. "I think it's retro back, which leaves him I think the 14th that he can come off. We'll just see where we're at. Yesterday, he didn't feel great. We've had this a few times this year where leading into his start there was a little soreness or whatever, but each time we've been able to get through it. Today, he woke up again and it just wasn't there, so we got Petit on a plane."
Johnson, who is 4-3 with a 3.81 ERA this season, struggled in his last start against the Los Angeles Dodgers last week. He gave up four runs (three earned) on six hits in just three innings.
"We DL'd him and his last start wasn't great, physically and performance-wise," Melvin said. "We were hoping that, after five days, he'd be that much further along and ready to pitch and that wasn't the case."
Johnson said this is the third time he's had a herniated disk.
"I had one 11 years ago," he said. "I had one at the end of last year. The same one from the end of last year got re-herniated. There's no telling how it happened. Other than maybe putting a lot of torque on my spine, which you are supposed to do when you pitch. I was throwing 95-97 [mph]. Maybe I put too much strain on it. I don't know. I'm not a doctor. I just play one on TV."
Johnson is becoming all-too-familiar with this particular kind of injury. He gave inquiring reporters a detailed explanation on Tuesday afternoon after having treatment on his sore back.
"What I have is a herniated disk, L-4, L-5, which is the second-lowest vertebrae in your back and the herniation is rubbing on my sciatic nerve," Johnson said. "The sciatic nerve runs down my leg and the sciatic nerve also controls the muscle impulses in your leg. If your sciatic nerve is not operating properly, it can't send the proper signals to the muscles to fire when they need to fire.
"So when I go out there to pitch, after a period of time, my leg isn't catching up with everything it's supposed to be doing. It becomes not strong, so it can't really support me. In the meantime, like today, I feel the nerve in my hamstring is grabbing, so it feels like there's a sharp knife going in my hamstring. That's just part of having a herniated disk. If we can get all that under control, hopefully I'll be able to get back to square one again, play catch, get on the mound and throw a simulated game and be able to pitch somewhere down the road."