Hernandez believes De Gea will continue to flourish at Old Trafford because he doesn't pay attention to the knockers.
"That's the way he is. He's very focused and doesn't listen to all that rubbish they speak about him.
"He has a lot of confidence from us and we tell him every day he's a very good keeper. He plays and enjoys it. He knows he can be the best in the world and for this club."