The keeper did not have the best of starts at United, but now he is turning into one of the best keepers around after pulling off some quite brilliant saves for the Reds.
But Fergie says his performances will get much better if he was to add a bit more weight to himself.
Ferguson said: "The boy has got talent. He's lightning quick but has just found it difficult to adjust to some parts of the game here.
"It's a matter of developing his frame. He's doing a lot of work in the gym.
"If we can get maybe a stone on him without losing any of his flexibility or speed it would be a great boost to him."