American midfielder Brek Shea injured his left knee in his first game of the preseason for Stoke, two days after scoring the U.S. goal that beat Panama in the CONCACAF Gold Cup final.
Shea helped set up Michael Kightly's goal in the fourth minute and scored in the 19th minute of Stoke's 2-0 exhibition win at Major League Soccer's Philadelphia Union Tuesday night.
The 23-year-old American was hurt from a tackle by Philadelphia's Matt Kassel and left the game in the 33rd.
"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," Stoke manager Mark Hughes was quoted as saying by Stoke's website. "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."
Hughes said Shea was to have an MRI on Wednesday.
"We know that we will definitely be without him for a number of weeks," the manager said. "It looks fairly serious, but fingers crossed it isn't any more serious than we already know it is."