The 27-year-old playmaker showed flashes of quality in his debut against Sunderland, and Pires believes that there is more to come from the Spanish international.
He told the club's official magazine: "Santi called me when the offer from the club arrived and I told him that it was the perfect club for him.
"The way the team plays will suit him perfectly and he is the kind of player Arsene Wenger loves too.
"His vision and the quality of his passing is brilliant but he can also take people on. He will need a bit of time to settle but I'm convinced he will adapt very quickly and will be a great signing for Arsenal."
Arsenal travel to Stoke City on Sunday, August 26 looking for their first victory of the season.