Ferguson admits the Mexican has exceeded all expectations.
"Hernandez has exceeded all expectations. He's a real threat," said Ferguson.
"The boy is keen to learn the game and perceptive to information. When he came at first we thought 'give him a year' but he has taken all the chances.
"I remember after Paul Scholes had seen him in training, he said the lad would get 25 goals for us as a sub.
"He's not quite achieved that but there are three games to go!"