Sunderland's Aji Alese has suffered an injury setback and has undergone surgery.
The 22-year-old was restricted to just 17 league starts last term with a thigh issue seeing him spend two months on the sidelines in the latter part of the campaign.
The centre-half, who arrived from West Ham last summer, did return to the fold for the second leg of the Championship play-off semi-final against Luton Town at Kenilworth Road. But he now appears to have suffered another setback.
