Ferguson: Ronaldo move was inevitable
United accepted a world-record 80-million-pound bid for the Portuguese winger on Thursday with the deal expected to be completed before the end of the month.
"He wanted to leave, it's as simple as that," Ferguson told the Mail on Sunday newspaper. "He was going to go some time. We've done well to keep him for so long."
Ferguson managed to keep Ronaldo at Old Trafford last season after Real had tried to sign him but the player, who scored 68 goals in his last two seasons for the Premier League champions, had often stated his desire to play for the Spanish giants.
United's former assistant manager Carlos Queiroz, now coach of the Portugal national side, said Ronaldo should not be criticised for deciding to leave.
"In the modern game, loyalty is to be a great professional, to be committed to your club and its goals and ambitions. In that respect, nobody can point one finger against Cristiano because, as a professional, he is brilliant."