Last season was regarded one of the best of Ferdinand's career, but he admits having previous doubts due to his injury woes.
"At times when I was having problems with my back and groin I did worry about it and wonder if I would ever be right again," he told the Manchester Evening News.
"There were many times when I couldn't see the light at the end of the tunnel and that bothers you.
"There were very dark days when you begin to question would I ever get back to the standard that I had become known for?
"There was a big part of me that wanted to prove people wrong."