Boss David Moyes said: "The situation is a big concern for the club and for Duncan.
"He has already had one injection to treat the injury
"The problem with the kind of injection is that he cannot train for five days after the treatment. We wanted him to have another this week but he said no because he wants to keep going in training. "
"If he had a second injection then that would be as far as we could go."
Ferguson is due to play for the reserves next week, and if he comes through that there is hope, but if he doesn't the club may be tempted to take the insurance money whilst they can.
Ferguson is due to play for the reserves next week, and if he comes through that there is hope, but if he doesn't the club may be tempted to take the insurance money whilst they can.