Sunderland midfielder Darron Gibson is facing up to 10 weeks on the sidelines as he waits to discover whether he will need groin surgery.
Manager Chris Coleman said after Monday's 1-0 Championship defeat to Barnsley that Republic of Ireland international Gibson had aggravated a persistent problem and could be out for some time, with his fears confirmed by a scan.
Coleman told a press conference: "He's low, he's down because in the way we want to play, he's been key, really, and he was definitely grasping what we need from the holding midfielder in the formation we want to go with.
"Now we've lost him for eight weeks, 10 weeks possibly, and that's a big blow. It's a tough one.
"We are going to get one more opinion -- we have had two and we are going to get one more opinion just to make sure -- but we think it's going probably eight to 10 weeks he's going to be unavailable, which is a huge blow for us."
Former Manchester United and Everton player Gibson, 30, had been enjoying perhaps his best run for the club when misfortune struck.
Coleman also has doubts over midfielders Paddy McNair and Aiden McGeady for Saturday's FA Cup third-round tie at Middlesbrough, while Lee Cattermole, Didier Ndong, Jack Rodwell, Jonny Williams have been ruled out.