The 36-year-old, who signed a new one-year contract earlier this summer, was hurt in a collision with goalkeeper Nikola Milojevic in Wednesday night's 1-1 draw with Vitoria de Setubal in Portugal.

It was initially hoped the former Manchester United star had only suffered bruising, but he will now undergo X-rays with medical staff fearing the worst.

Manager Roy Keane told the club's official website: "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."

Sunderland's first match of the Barclays Premier League season is against Liverpool.

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