McGowan attempted to throw off flat ground on Wednesday morning, but the lingering discomfort caused problems with his mechanics. As a result, the Blue Jays have opted to limit McGowan's activity until he is deemed fully healthy.
"He felt like his arm slot would begin to vary a little bit, and that is the one telltale sign that we'll stay away from -- any variation from that putting the additional stress on the throwing motion," Blue Jays manager John Farrell said.
McGowan was expected to open the season as Toronto's No. 5 starter, but it now appears unlikely that he will be ready to go. That has opened the door for 24-year-old Kyle Drabek to break camp with the team.
Toronto has three off-days in the first two weeks of the season, which means the club would only need to go with a fifth starter once prior to April 21.