McGowan has been sidelined since March 26 after being diagnosed with plantar fasciitis. He will not throw for at least the next five-to-seven days and will then need to start building his arm back into game shape once given a clean bill of health.
Blue Jays manager John Farrell estimated that whatever time McGowan ends up missing, before beginning to throw, it will take the same period of days to rehab from the injury.
"Let's say he misses two and a half weeks, he'll need two and a half more weeks to get back to the game status he was in when he came out," Farrell said.
"I would think at a minimum [two rehab starts]. We're certainly not going to rush anything. As I stated the other day, you get any kind of foot or leg injury we don't want that to show up in his shoulder and we'll take every precaution needed."
McGowan was set to start the season as Toronto's No. 5 starter. He returned last September following a three-year absence because of multiple surgeries and proceeded to go 0-2 with a 6.43 ERA in 21 innings.