Sunderland are bracing themselves for the news that Wes Brown will not play again this season.
Brown is now undergoing a series of sugar injections in the hope of curing the long-standing problem, although no specific time frame on his return has been announced.
"Wes is feeling really frustrated with it all," said boss Martin O'Neill.
"He just has ten or so days where he thinks he is going well and then gets a setback.
"He has these injections, a course of sugar injections, which are making him feel better at the minute. He feels they are benefiting him and I think the lad (Stoke City captain Ryan) Shawcross had them some time back.
"We have lost his services and it has got to the stage where we can't even consider him. It is bad for us, so it must be terrible for him."