Johnson, who was scratched from a scheduled game appearance on Saturday, was diagnosed with a strained rotator cuff and tendinitis in the supraspinatus tendon in his pitching shoulder. He underwent an MRI exam on Monday and got the results on Tuesday. He had been expecting the worst, so the diagnosis came as good news.
"Great news," Johnson said. "I don't have to have surgery. Any time you don't have to have surgery, it's great news. I wasn't sure if it was that bad, anyway. I was just feeling tired and a little weak. But I know now that there's nothing wrong, and I can go out there and do what I have to do."
General manager John Mozeliak said that the MRI results will be sent to Dr. Lewis Yocum for second opinion in order to confirm the diagnosis as well as the plan of action.
"We'll have his MRI looked at by another doctor," Mozeliak said. "At this time, though, it is very favorable news. It appears that through some medication and also through some strengthening and stretching he should be back to where he can start throwing again."
Both Johnson and pitching coach Dave Duncan speculated that the problems may have resulted from Johnson trying to do too much, too fast.
"He said he had been throwing, and I was actually surprised that he threw the ball as good as he did," Duncan said. "Maybe he overdid it. He probably did a little too much early on. Put too much into it."
Though Johnson will be kept off a mound, he may throw some long toss while he is recuperating.
"I'm going to strengthen for that week," he said. "It's not that I can't throw, it's just that they want me to [work on] arm strength."
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.