The Angels placed Johnson on the 15-day injured list Monday with a viral infection.
Johnson had to be scratched from a scheduled start Sunday against the Mariners and has not made enough strides in his recovery to avoid a stint on the IL. He'll be eligible to return later this month and should be physically ready then, though it's not a given that Johnson will be re-inserted into the big-league rotation at that point. George Klassen should remain in the Angels' rotation while Johnson is shelved.