Louis van Gaal has admitted to not being entirely convinced by goalkeeper David De Gea at the start of his Manchester United tenure.
De Gea, 24, enjoyed an excellent season for United, helping the club secure Champions League qualification with their fourth-placed finish.
The Spain international's form has led to interest from Real Madrid, with Van Gaal conceding he could lose the shot-stopper.
Former Netherlands boss Van Gaal said of De Gea in The Times: "He has made very good development this year because in the beginning I was not so sure of him.
"But now he is fantastic and has saved us a lot of times."
De Gea signed for United from Atletico Madrid for £18 million in 2011 and he has since made 131 Premier League starts for the club.
The goalkeeper finished third in the voting for the PFA Player of the Year award and was voted by fans as United's outstanding individual this season.