"We are all concerned," said the United chief.
"He has not played for over two years so we would have to be super-optimistic to think everything in the garden was rosy about him making comebacks.
"What we are trying to do is help the lad. That in itself is our biggest challenge. We want to help the lad try to get back to a level where he can still play football."
"This hamstring injury is a real kick in the teeth," said Ferguson.
"He was doing so well in training before the Wolves game. He was absolutely superb.
"There were no qualms whatsoever about putting him in, even though he had only trained for nine days.
"We were confident enough to play him but unfortunately it has proved to be a disappointment for us.
"If he had realised early enough and come off before he had done any more damage, it could have been three to four weeks. But is a complete tear."