David de Gea believes he is a far superior goalkeeper after a season-and-a-half at Manchester United.
The former Atletico Madrid shot-stopper signed for United for £17 million in 2011 but has been dropped for Anders Lindegaard in both of his two campaigns at Old Trafford.
However, he returns to his home city to face Real Madrid in the Champions League having re-established himself as United's first-choice 'keeper and confident that he has progressed.
"When you arrive at a new club it is normal there will be low points," he said. "The important thing is to learn from them and improve. I know I am much better than when I first arrived at Manchester United."
De Gea's future is uncertain with Sir Alex Ferguson scouting Stoke's in-form goalkeeper Asmir Begovic on Saturday and the Spaniard linked with a return to his native country in the summer.
But while De Gea has been blamed for several goals United have conceded this season, Ferguson feels that is unfair.
He said: "David has shown his character because he has taken a lot of criticism, sometimes unfairly.
"What we are good at is developing people. He came to us as a very young man, not used to the English game and unable to speak the language.
"Also he was still to mature physically. But it's like a young kid taking his first steps forward, he wobbles, then gets up, wobbles, then gets up again and eventually he walks. The boy is walking now."
De Gea is a Spain Under-23 international while Real can normally call upon the services of Spain's World Cup-winning captain in goal.
But the injured Iker Casillas will miss the tie with United and De Gea added: "Every time Iker Casillas is not there he is a great loss. They have two other keepers who can do it as well as he does. But it is still a great loss."