De Gea was expected to complete a move to Real on Monday, but the paperwork was not completed in time and so the Spain goalkeeper remains at Old Trafford.
Real president Perez was baffled by United’s failure to conclude the deal, which would have seen Keylor Navas move in the opposite direction, and is not surprised the likes of Pedro reportedly turned them down.
He told Cadena SER: “At 1330 Manchester United had all the papers but they took eight hours to return them.
“It’s very unfortunate and I don’t want to blame anyone but we don’t understand why it took them so long to send them, or why they only decided to negotiate when there was 12 hours to go.
“I don’t think they had bad intentions, I just think they lack experience as the same thing happened with [Fabio] Coentrao and with [Ander] Herrera [attempted United signings which failed two years ago].
“When this happens more than once and you see that all the operations that, according to the media, they have tried to do during the summer one believes that this happened because it is a new team with no experience.”
Perez also stated that it is too early to say if a deal to bring De Gea back to the Spanish capital can be resurrected.
He added: “More than a year ago we decided that the future replacement for [Iker] Casillas was De Gea. Then Keylor Navas signed and we were very happy with him but we had already made a commitment with De Gea,
“I don’t know what will happen now, we can’t say what will happen because such little time has passed. I haven’t spoken to him but [Real chief executive] Jose Angel Sanchez has. He is very upset because he was really excited about joining Madrid.”