Pires told the Daily Star: "Santi called me when the offer from Arsenal 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 loves, too.
"He is a very exciting player, very gifted technically and good with both feet. He has an impressive creative touch and he can play in the centre or on the wings.
"His vision and the quality of his passing is brilliant but he can also take people on.
"Despite still being quite young, he has big experience with the Spanish national team and has also played in the Champions League.
"Finally, he has a very good mentality and is a real team player. He will need a bit of time to settle but I'm convinced he will adapt very quickly and prove to be a great Arsenal signing."