Wigan fear forward Victor Moses could be out for up to three months after dislocating his shoulder in Tuesday's defeat at Arsenal.
The club initially anticipated a four to six-week lay-off for the 19-year-old after he injured himself landing awkwardly in a tackle during the 2-0 Carling Cup loss.
Further examinations have now shown the injury to be worse than thought and the former Crystal Palace playmaker is likely to be out until spring.
Latics manager Roberto Martinez said: "It is a huge setback. We haven't got the final assessment but we fear the worst.
"It seems it could be the best part of three months that we are going to miss Victor.
"It is a real blow. He has worked hard to earn his place in the side and he has done that with real style. You could see slowly he was imposing himself.
"Now he has been knocked back by an injury but we will make sure he comes back ready to have big say in the final three months of the campaign."
Moses joins midfielder James McCarthy on the long-term injury list.
McCarthy is expected to be out until the end of January after undergoing knee surgery.
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