Speaking to The Guardian, Ferguson praised Ronaldo unreservedly, saying, "His best is yet to come because he is just 24.
"I will be very proud when I see [him at his best] because we had a part to play in it. He came to the right club at the right part of his career.
"He could have gone to Real Madrid or Barcelona as a boy but he came to the right club and he appreciates that.
"And he may come back, you never know."
Ferguson then expressed how much Ronaldo loved the Red Devils, continuing, "I don't see it happening if things go wrong at Real Madrid necessarily, but he loved Manchester United so it may happen.