Sunderland boss Mick McCarthy says defender George McCartney will undergo surgery on his hamstring problem that will rule him out for up to six months.
McCartney, 24, has had the problem for 10 months and decided to go under the knife after seeing a specialist.
Boss McCarthy told the club website: "We have taken every conservative measure to solve the problem and the last course of action was surgery.
"Hopefully it will put an end to what has been a frustrating injury."
The full-back visited specialist Dr Nic Maffuli at the North Staffordshire Infirmary to ascertain the best course of action.
He will have the operation on Monday and is unlikely to be back within four months.