The West Londoners finished ninth in their second Premier League campaign and signed Dutch goalkeeper Mark Flekken from Bundesliga side Freiburg on a four-year contract in May.
Raya has been with Brentford since they were in the Championship (second tier).
Media reports have spoken of a loan deal for an initial 3 million pounds ($3.81 million), with an option for a permanent transfer for 27 million, to provide competition for England keeper Aaron Ramsdale.
"I expect the deal will be completed with Arsenal. He’s not here at the moment and won’t be involved on Sunday," said Frank.
"Mark Flekken was one of the best keepers in the Bundesliga last year. I like his personality; he is a leader. I like his distribution and dominance in the area. From the first game in America to Lille, he has got better each time."
