Alonso was an unused substitute in Besiktas and he could well make a return against Arsenal after an eight game absence.
"It's clear that with Xabi, Daniel Agger or Fabio Aurelio, players with quality in possession, you can improve your attack," said Benitez. "The question is to find the balance. Xabi is a top class player. If he plays well then the team plays well.
"In midfield we have Gerrard now playing better and if you have Steve, Mascherano or Xabi playing well then you know the team will play better.
"Xabi can play with pace. He has pace with the ball. It's important that we have someone who can switch the play before the opposing defenders are organised, he can pass the ball 40 yards so the defenders don't have time. Sometimes you need a player like Xabi."