Alonso left Liverpool and joined Real Madrid this summer, while Aquilani joined the Reds from Roma.
Benitez said: “Alberto is running again and when we travel to play Fiorentina in the Champions League this week he will stay behind to continue with his rehabilitation programme.
“I know the fans are frustrated but we have signed a good player with talent and I never worried that we would have to wait for him to be fit.
“Xabi was a player who received the ball and played long and short passes. Aquilani wants to play higher up the pitch than that.
“He wants to be in the final third so that he can create chances.
“In that respect, playing passes to give the strikers the chance to score, he is better than Alonso.
“When he is fit the team will be more dangerous because he has the ability to find Torres and Gerrard with passes that will give them more chances to score.
“He is ahead of schedule for his comeback, but we must be careful with him.”
