Darron Gibson has been ruled out for eight to ten weeks due to a groin injury, Chris Coleman has confirmed.
The Republic of Ireland midfielder has flourished under the Welshman, putting in a string of consistent performances to become a key member of the starting XI.
But he now faces an extended spell in the treatment room – and potential surgery – with a third specialist set to take a look at the injury before the club plan his recovery.
“It’s a big blow and tough one,” said Coleman when asked about Gibson. “We’re going to get one more opinion – we’ve had two – but we think it will be eight to ten weeks.
“There’s a little bit of doubt about whether it’s completely off the bone, so if it is it’ll be surgery, but if not we could get him back a little quicker.”
Meanwhile, Aiden McGeady and Paddy McNair have both been rated as doubts for Saturday’s Emirates FA Cup tie at Middlesbrough.
Adam Matthews is also set to miss the game after playing in all the Black Cats’ festive fixtures, meaning the Black Cats could be without up to 12* first-team players.
“Paddy McNair trained today but there is a doubt with him as he has a reoccurring problem with his groin and his stomach, so we’ll have to assess him tomorrow to see if he can play any part on Saturday.
“Aiden McGeady has a problem with his calf; he also trained today but again we’ll have to see how he is tomorrow, and Adam Matthews is a no on the back of two games in three days and a problem with his calf.”
He added: "We still have the rest of guys who are going to be out for some time.
“Goochy will be out for another seven to ten days so our bench on the weekend will mainly be academy boys, as at the last count it was nine or ten players unavailable.”
*Lamine Kone, Matthews, Lee Cattermole, Gibson, McNair, Didier Ndong, Jack Rodwell, Jonny Williams, McGeady, Duncan Watmore, Lynden Gooch, Lewis Grabban.