Here is a scouting report of Navas, a 27-year-old, 6'0", 172-pound Costa Rican international.
Navas accumulated a higher amount of saves, catches and punched clearances per 90 minutes than Lopez and Casillas last season, according to Squawka.
Being a game-saver is why Navas can become a crucial component of Real president Florentino Perez's latest Galacticos era.
Almeria substitute Oscar Diaz's scorched shot was saved adroitly by Navas, who ensured Levante held on to a 1-0 victory.
Displaying razor-sharp reflexes, Navas denied close-range headers from Espanyol centre-back Hector Moreno and Granada centre-forward Youssef El-Arabi.
Quickly rearranging his position in response to a deflection, Navas thwarted Atleti defender Toby Alderweireld's firmly hit shot.
Commitment is a trait inherent in Navas and evident when he clattered into his post after punching away the free-kick of Elche right-back Damian Suarez.
His penalty-saving ability lends further credence to Navas' status as a world-class goalkeeper.
He came up big to stop then-Barcelona (now New York City FC) centre-forward David Villa, Real Betis centre-forward Jorge Molina and Greek centre-forward Theofanis Gekas from 12 yards out.
Mistakes precipitated Casillas' downfall and it could be the same scenario for Navas.
Buried beneath the profusion of acrobatic saves, Navas' tendency to make errors is a red flag.
He crashed into Molina to give away a soft penalty to Betis—which he ended up saving.
Navas inadvertently kneed Villarreal centre-forward Ikechukwu Uche, which led to a penalty and a red card.
A hasty attempt at a clearance enabled Malaga attacking midfielder Francisco Portillo to score.
There are still unanswered questions over Lopez's future at Real, per Ramon Fuentes at Marca:
The Spanish 'keeper [Lopez] does not want to leave Real Madrid with the way things stand at the moment. ...
According to the initial agreement with the club, the keeper would receive around €7 million before tax (around €3.5 million net) on his departure. However, this may have changed and Real Madrid are now understood to only be willing to offer him a free transfer.
The second reason has to do with his destination. The player's preferred option was Monaco. He would have joined the French club as the first-choice 'keeper. However, the personal terms offered by Monaco did not convince either the player or his agent.
It would be Perez-esque extravagance if he brokered an agreement to keep Navas, Lopez and Casillas.
Real would have two world-class goalkeepers in Navas and Lopez, while Casillas is given a small window to mount a Rocky Balboa-like comeback.
Navas may not carry a Galacticos-like fee at €10 million (a transfer steal), but he has the ability to transition into a Galacticos-standard goalkeeper, which will inflict additional hardship on Casillas.
Statistics via WhoScored