Duncan Watmore could miss the start of pre-season after David Moyes revealed he has suffered a setback in his injury recovery.
Watmore suffered a cruciate injury to his knee last year and the Black Cats had hoped he would return to play a full part in pre-season.
Moyes said the 23-year-old had been experiencing discomfort as he steps up his recovery and will see a surgeon this week to see if further treatment is needed.
He said: "They’ve gone in to check his knee, it looks like his cartilage. He’s getting it looked at this week, we think at the moment, it might add an extra month on. It might mean that he doesn’t start pre-season but we will see."
It is a blow for Sunderland's planning towards next season, with Watmore likely to be one of a number of young players who Moyes will turn to should the Black Cats not manage to beat the drop.
Moyes remains hopeful that Paddy McNair will still return for pre-season as he recovers from a similar injury.
He said: "He’s [Watmore] one of the boys if you want to call them that, the young players that we’re trying to get around the squad. Obviously losing Duncan and Paddy was a blow, for the club and the team but for them as well. The idea was that well at least we’d get them back for pre-season, we will have to see."