The Reds only managed a 1-1 draw with Manchester City at Anfield on Sunday and are seven points adrift of leaders Manchester United.
“I think we will have to beat Manchester United now,” Benitez told Sky Sports.
“Clearly it is more difficult now. It is a bad result.
“We have to beat Middlesbrough and Sunderland and start thinking about if we can win at Old Trafford.
“You never know what can happen but clearly they can win games and win games without playing well.
“I have confidence that we can beat Middlesbrough and Sunderland and then it will be a different situation. There are still 12 games to go, you can’t say anything is finished.”