"It is particularly bad news for us. When he went off, I thought it was fairly serious. He is a tough lad - it takes a lot for him to come off," said Black Cats boss Roy Keane.
"We don't do things by halves at our club. The only silver lining is that we have a two-week break now with no games, but it's not much of a silver lining because if it does take six weeks he's going to miss some very important games for us."