Arash Madani is a reporter for Sportsnet Canada, and he's got more details in subsequent tweets:
Seeing Dr. James Andrews is never a good thing for a baseball player, particularly a pitcher; shoulder surgery could be in McGowan's future. After throwing for a while:
This wouldn't be the first time McGowan has missed time with shoulder injuries; he missed half of 2008 and all of 2009 with debridement surgery on his right shoulder. Returning to the major leagues in 2011, he made just five appearances with a 6.43 ERA. At 30, the time for him to have a productive major league career is growing short.
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