Johnson will undergo an MRI to determine the exact nature of his injury, but he has been at least temporarily shut down and there is no timetable for his return.
"Doctors are just taking a look at him now and they're going to send him for MRIs," general manager Alex Anthopoulos said early Tuesday evening. "Off the exams, structurally and things like that, it doesn't look serious, but he doesn't feel right."
Johnson first experienced the discomfort during his last start against the Mariners on Aug. 6. His scheduled outing Sunday was then pushed back a couple of days to provide some additional rest, and for awhile, it appeared as though everything was going to be fine.
That changed prior to Tuesday night's game against Red Sox. Johnson played catch and felt his forearm tighten up to the point where he believed it wouldn't be smart to continue throwing.
The injury couldn't have come at a worse time for Johnson, who went through weeks of struggles on the mound before finally figuring things out against Seattle. Johnson pitched five scoreless innings against the Mariners and had plenty of positives to take away from the outing, but none of that seems to matter now.
"Before the last start, that was the best I felt in three years," Johnson said. "Shoulder, elbow, everything felt right where it needed to be. I don't know what happened, but I came out of that start and I was a little sore and tight."
Even if the MRI results don't reveal any structural damage, Johnson will be hard-pressed to return before the end of the season. With only six weeks left in the season, Johnson would need to quickly recover and then at least pitch in a couple of simulated games before rejoining his teammates in Toronto.
Johnson said he felt the discomfort feels more related to a muscle than a ligament in his elbow. That's an encouraging sign and there will be plenty of incentives for the soon-to-be free agent to return for a start or two in September, but it will be a tough task to accomplish.
"That's the only thing I want to do is be on the mound," Johnson said. "Especially after how I felt in the last bullpen in the last game. That's the one thing I want to do, is get back out there, but this is holding me back for sure."
Johnson was acquired as one of the major components in a blockbuster trade with Miami during the offseason. His season was sidetracked early on with a right triceps injury and he wasn't able to get things figured out. The 29-year-old is 2-8 with a 6.20 ERA in his 16 starts this year.