A deadline-day deal for the 20-year-old midfielder fell through despite the clubs agreeing a fee and Ferguson explained how close they were to signing the Scotland Under-21 international.
"We couldn't agree personal terms," he told BBC Radio Cambridgeshire.
"We were very close. I put a lot of effort into this one and unfortunately it's not been done. I'm really disappointed.
"There's a good chance there'll be others in for him now. That was the advantage of getting him now.
"Wolves were very interested but he wanted to come here."