The Marlins' 23-year-old right-hander underwent a series of nerve tests in Jupiter on Monday.
While the Marlins now must brace for life without one of their top young starters, the encouraging news is the medical staff is confident Johnson won't need surgery.
"It's better than three months," said Johnson, who had a chance to be the Marlins' No. 2 starter. "I knew I wouldn't be out the whole year."
The injury is similar to what Dodgers right-hander Brad Penny had in 2004. Penny missed a majority of the second half of that year.
Johnson added that medical personnel told him this injury should heal itself.
The Marlins open the regular season on April 2 at Washington. The earliest realistic date of Johnson returning would be around June 1.
From the information he received, manager Fredi Gonzalez was not surprised that Johnson would return in 2007.
"I never took it that it would be season-ending," manager Fredi Gonzalez said.
Gonzalez added that when Johnson is cleared to throw, the plan is to have the 6-foot-7 right-hander work his way back to full strength as a starter. Another option would be to use him out of the bullpen, but the team is not leaning that way.
Johnson experienced discomfort in his biceps/triceps area while throwing off flat ground on Jan. 19. He has thrown twice since, but after feeling discomfort again on Feb. 22., he was shut down.
Since then, the Oklahoma native dealt with uncertainty. Now he can take comfort knowing exactly what is bothering him.
"It's a lot easier. I just know. It's good to know," Johnson said. "I know exactly what it is. Now, I can hopefully set a timetable."
At least early on, Johnson had peace of mind that he wasn't bothered by ligament damage. Several MRIs showed the ligament was fine and that he didn't have any stress fractures.
Johnson had an MRI taken by Dr. James Andrews in Birmingham, Ala., and he had a couple of MRIs and a bone scan taken last week.
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 in which he re-entered the game after an 82-minute rain delay. He experienced forearm tightness that night, and he hasn't thrown off a mound since.
Johnson says he doesn't think his Sept. 12 start had anything to do with his current injury.
"I doubt it," he said. "I went through the whole throwing program in the offseason."
While Johnson is downplaying publicly what happened on Sept. 12, player and team sources privately questioned then-manager Joe Girardi's decision to return the rookie to the mound.
Johnson had no arm problems before that start, and the right-hander had never returned to the mound after a rain delay. Besides the 82-minute delay during the game, the start time that evening was held back 45 minutes because of the weather.
In that game, play stopped with the Mets batting in the top of the second inning. About 20 minutes into the delay, Dontrelle Willis advised Johnson to stay loose by playing catch. That was the only time Johnson picked up a ball during the stoppage.
Johnson threw 157 innings in 2006 and was five innings shy of qualifying for the National League ERA title.
With Johnson out, Gonzalez said the field is "wide open" for the fifth starter spot.
If healthy, Sergio Mitre is a frontrunner. Mitre threw a simulated game on Tuesday, and he is in line to pitch in Grapefruit League action on Sunday against the Mets at Port St. Lucie.
Yusmeiro Petit, Wes Obermueller, Chris George and Jose Garcia are options as well.
The Marlins plan on carrying 12 pitchers, and because of an April 5 off-day, they could go without a fifth starter until April 11 against the Brewers.
The projected first four starters are Willis, Anibal Sanchez, Scott Olsen and Ricky Nolasco. Nolasco, who was scratched from a start on Monday because of back spasms, is expected to make his next start on Saturday against the Dodgers.
"Anybody in camp could conceivably be in the rotation," Gonzalez said.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.