The Spain international is believed to have cost the Gunners £3m for the current campaign, and the club are expected to sign him permanently for around £27m next summer.
Raya becomes Arsenal's fourth signing of the summer window, following Jurrien Timber, Declan Rice and Kai Havertz to the club as he prepares to engage in a fierce battle with Aaron Ramsdale for the number one jersey.
«I'm over the moon to be able to take this challenge in my career and make the step up,» Raya told Arsenal's media channels. «I'm really excited to get going and see how the season ends up.
»I spoke to the boss and he sent me the values of what Arsenal are about. The way that the club is going, it's growing even more so it is a beautiful challenge to take and I couldn't say no.
«I've seen Arsenal a lot for a lot of years and since [Mikel] came he's made a massive difference to the style of play and to the club. The way the team plays out of the back, being confident and taking possession to the other team is the main thing why I fit into the team. I'm going to try and help as much as possible and we'll see what happens.
»I can't wait to be out there training with the lads and getting that GK union going. That's a tight group that we're always going to get along and push each other, so that's going to be a healthy group in my opinion. I just can't wait to get going and meet the lads."
Raya has played a crucial role in Brentford's rise from the Championship to the top half of the Premier League table, keeping 54 clean sheets in 161 games and making more saves than any other goalkeeper in
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