Shea is set to undergo a scan on Wednesday to determine the full extent of the injury suffered in the club's final game of a pre-season tour in the United States, although manager Mark Hughes has warned fans that it "looks fairly serious".
The 23-year-old United States international linked up with his Stoke team-mates after scoring the only goal in Sunday's CONCACAF Gold Cup final against Panama.
Shea followed that goal with Stoke's second against Philadelphia Union before being on the receiving end of a reckless first-half challenge from Matt Kassel that leaves him a major doubt for the start of the Premier League season.
Hughes confirmed to the club's official website: "He will go for a scan (on Wednesday), but we know that we will definitely be without him for a number of weeks.
"It looks fairly serious, but fingers crossed it isn’t any more serious than we already know it is."
Kassel's tackle 10 minutes before half-time left Hughes fuming, as he added: "It’s incredibly frustrating and hugely disappointing to lose Brek, especially in a game like this where you would expect players to look after their fellow professionals.
"I really have no idea what the lad was thinking about by going in for the challenge like that.
"Maybe he was trying to make a name for himself, I have no idea, but whatever he was thinking it was totally wrong.
"We have been waiting a while to get Brek back here, and up until the injury he looked very bright, very dangerous and appeared to have a real understanding of what his role was on the left hand side of midfield."
Shea joined Stoke from FC Dallas in January, but has made just two competitive appearances.
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