Sir Alex Ferguson believes it is not beyond the realms of possibility Cristiano Ronaldo will one day wear Manchester United colours again.
The Portuguese wide man kicked off his Real Madrid career on Monday night as he made his first start in white in a pre-season friendly against Shamrock Rovers.
A world record £80million fee was needed to tempt United into a sale over the summer as Ronaldo fulfilled his childhood dream of playing for the Spanish titans.
Ferguson accepts that after six magnificent years' service at Old Trafford the 24-year-old had earned the right to join his boyhood club.
And while Ferguson does feel the winger will prosper at the Bernabeu, he cannot entirely discount the possibility of Ronaldo eventually coming back to Manchester.
"He may come back, you never know," said Ferguson. "Sometimes it happens that way.
"He loved United. If you look back at the six years he had with us, he never missed training.
"That's one of the things he has above all other players - he was never injured, he always played.
"And his best is yet to come. He is only 24."
While some United supporters have speculated Ronaldo's exit will allow Wayne Rooney to flourish as the team's creative epicentre, Ferguson accepts losing his chief goalscorer, a player he ranks as the world's finest, has left a significant void.
"Cristiano is a massive loss," conceded Ferguson.
"I have nothing but praise for the boy. He is easily the best player in the world.
"He is better than Kaka and better than Messi. He is streets ahead of them all.
"His contribution as a goal threat is unbelievable. His stats are incredible. Strikes at goal, attempts on goal, raids into the penalty box, headers. It is all there. Absolutely astounding."