Johnson was eligible to come off the disabled list next week and he hasn't pitched since April 21.
"He's started playing catch, feeling better," Jays general manager Alex Anthopoulos said to MLB.com. "We're hopeful to get him into a rehab game starting on the 21st [of May]. That's not set in stone, but that's kind of the date that we've had."Johnson, 29, is 0-1 with a 6.86 ERA, 1.88 WHIP and 2.11 K/BB ratio in four starts this season.