Van Persie joined United in a £25million deal from Arsenal last summer.
But he revealed that he blew a golden chance to go to Old Trafford even before Arsene Wenger brought him to England.
"But I was sent off that afternoon and the scout went back to England with that in his report. Sir Alex mentioned that to me when I arrived at United.
"He felt I was not yet ready for a move to a big English club all those years ago - and he was right.
"I said to the boss 'you were right then, but I am ready now'."