That is actually not true, Navas is a very good keeper and would be a great replacement for us with little time to do anything else. He's much better than Romero or Johnstone, even Madrid fans want him to stay.
He doesn't have the ceiling De Gea does but Navas is quality goalkeeper nonetheless.
Navas would be a great replacement regardless tbh.
Considering how much LVG likes Navas, United simply must end the window with him in the side.