Dwight Yorke could be doubtful for the start of the season after suffering a suspected fractured cheekbone.
The 36-year-old midfielder, who recently signed a new deal to keep him at the Stadium of Light, was hurt in a collision with goalkeeper Nikola Milojevic in Wednesday night's 1-1 draw with Vitoria de Setubal in Portugal.
Sunderland had initially hoped it was just bruising but it now seems the injury could be more serious.
Yorke is set to undergo X-rays and manager Roy Keane admits he could be facing a spell on the sidelines.
The Black Cats kick off their Premier League campaign against Liverpool on 16th August and Keane will want one of his most experienced players to be fully fit.
"We thought it was just a bang on the head, but there could be a fracture there, around his eye," Keane told the club's official website.
"He will be out for a number of weeks."