"George is not right. At the minute the injury has just got to settle down," the Sunderland boss told the clubs official website.
"He's had this problem with his tendon at the bottom of his hamstring. He's been for scans and we're having it looked at but he's not going to be fit for the start of the season.
"We think he may have just torn it a little and that might be a positive thing because it has been grumbling on for a long time. If it has