The 22-year old Spanish goalkeeper has had his ups and downs since joining from Atletico Madrid in the summer of 2011 but Ferguson suggests he is on the way to really finding his feet at Old Trafford.
"The boy has shown his character," Ferguson said. "He has taken a lot of criticism and a lot of it unfair.
"What we are good at [at United] is developing people. [He was] a young man, very young, not used to the English game, who couldn't speak the language and still had to mature physically. But it's a like a young kid taking his first steps forward.
"He wobbles, gets up, wobbles, gets up again and eventually he walks. The boy is walking now."