Fri Jul 25, 1:08 PM ET
Yorke, 36, was hurt in a collision with goalkeeper Nikola Milojevic in Wednesday's draw against Vitoria Setubal in Portugal.
The former Manchester United star, who signed a new one-year contract at the end of last season, will now have X-rays to determine the full extent of the injury.
"We thought it was just a bang on the head, but there could be a fracture there, around his eye. He will be out for a number of weeks," Black Cats boss Roy Keane said.
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