The right-handed McGowan, who pitched only four innings in his Tuesday start before being removed, underwent an MRI on Wednesday, which showed he is suffering from a tear in his right rotator cuff.
He will visit specialist Dr. Timothy Kremchek at some point in the coming days to get a further idea of the injury and decide whether surgery is needed or not.
According to Jays general manager J.P. Ricciardi, Kremchek will compare film of McGowan's shoulder this year to that of previous years in order to get an idea of the severity of the tear.
"I think right now, we're probably looking at, I don't know exactly how long, but probably longer than four weeks," Ricciardi said, regarding how much time the pitcher could miss.
"We're not anticipating anything good or bad at this point," said the GM. "We're just going to have him see Kremchek and see what his thoughts are and hopefully we'll be able to rehab it and get [McGowan] back."
With McGowan on the DL, the Jays recalled right-hander Brian Wolfe from Triple-A Syracuse. As well, the team has also shuffled its rotation in light of the injury.
Left-hander John Parrish will now start on Thursday in the series finale against Baltimore. Then, for the upcoming series against the Yankees, the Toronto rotation will set up with Roy Halladay pitching Friday's game, Jesse Litsch on Saturday and reliever Brian Tallet taking McGowan's spot in the rotation on Sunday.
Halladay and Litsch will now both have an extra day's rest from their last starts. Ricciardi said the decision to push the two pitchers back a day was made because the Jays would like to have Halladay pitch against the Yankees instead of the Orioles.
Ricciardi also said that the Jays plan to use Tallet as a starter only for Sunday's game. He did hint though, that the Jays may consider bringing up left-handed starter David Purcey from Syracuse following the All-Star break.
The Jays GM was also able to shed some light on Shaun Marcum, another injured Blue Jays starter. Though Ricciardi did say that Marcum was still set to rejoin the Jays after the All-Star break, the GM remained cautious.
"We don't know," said Ricciardi. "Stranger things have happened. Right now, he's on pace to pitch in Baltimore, but we'll see. It's a long way from then."
Ricciardi said Marcum will pitch in a Minor League game on July 16. The plan is to have him make the one Minor League start and then rejoin the Toronto rotation during the July 21-24 series in Baltimore.
David Singh is an associate reporter for MLB.com This story was not subject to the approval of Major League Baseball or its clubs.