"They think it's probably a nerve thing," Matt Sosnick, Johnson's agent, told The Associated Press. "The worst-case scenario is probably that he would be out eight to 12 weeks, but they have to figure out what this thing is."
For days there was a growing fear that Johnson was plagued by a nerve problem in his elbow/biceps area.
The results of three MRIs showed there was no ligament or rotator cuff problems. A bone scan also came back normal, according to Sosnick.
Projected as one of the Marlins' top three starters, Johnson may miss a significant portion of the season. If surgery is required, he likely would be lost for the year.
Johnson experienced discomfort in his biceps/triceps area while throwing off flat ground on Jan. 19. He has thrown twice since, but after again feeling something wasn't right, he has been shut down.
As a rookie in 2006, the right-hander was 12-7 with a 3.10 ERA. His season was cut short after a Sept. 12 start, during which he re-entered the game after an 82-minute rain delay. He experienced forearm tightness that night, and he hasn't thrown off the mound since.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.