#2 Kiko Casilla
One prominent reason why Keylor Navas's mistakes have been neglected by Real Madrid's hierarchy is due to the lack of competition he faces from Kiko Casilla. Real Madrid signed Kiko Casilla as the replacement of outgoing Iker Casillas, but he has failed to fill into the shoes of the latter. Casilla is a decent goalkeeper and he would do quite well if he played for any other team in the division but still he isn't the top quality material needed for Real Madrid.
Real Madrid have always been known for having top class goalkeepers like Casillas, Bodo Illgner, Ricardo Zamora, Jose Banon et al. Footballing History has always been glorified by the presence of these legends, but Casilla have been substandard when compared to them.
Buying a replacement for Casilla also might help in improving the performances of Navas who a pretty good keeper, in fairness.