Ferdinand spoke out about the Spanish keeper after he put in a man of the match performance in the Red Devils' 0-0 draw with Sevilla in the Champions League on Wednesday.
"We were talking before, when he first came, even as players we were sitting there with doubts really," said Ferdinand.
"A young kid just coming to Manchester United, and we needed to win every year.
"How were we going to do that with a young kid, who was inexperienced and looked like he was lacking confidence?
"But you look where he is today and that's a sign of someone who has worked hard to get where he needs to get."