"If they (Arsenal) want to win a trophy then it must be this game because it will be very difficult to win the Premier League," said the Spanish coach.
"Before the game on Saturday they knew they had to win to stay in the title race.
"He (Arsene Wenger) changed five players, but had to bring back his big players trying to win the game.
"Maybe afterwards he felt that the race for the title is over. But then United drew at Middlesbrough, so he will maybe think that their chance has returned.
"But I still believe this game at Anfield will be the most important match they have if they want to win a trophy."
Benitez added: "We are confident. We have been playing well in recent games and have been getting the results. The performances have been good. That is what we have been looking for at this stage of the season.
"The Champions League is massive for them though, that is what they will be thinking about.
"And for us, we need to score. Arsenal can always score away so we cannot think of a 0-0."
