Raya, one of Brentford's standout performers so far this season, was this week ruled out for up to five months with a knee injury.
And Fernandez says he'll be ready after helping the Bees into the quarter-finals of the Carabao Cup with a 2-1 victory at Stoke.
“First of all I wish David a good recovery," the 23-year-old said of his fellow Spaniard. “We are team-mates but friends as well, we work every day to play.
“Now it's a good opportunity for me, I'm going to try my best and in football you have to be ready always. I've worked everyday as hard as possible and I'm ready so let's go."
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