"For sure it will be the real test of where we are at the moment," the Brazilian told liverpoolfc.tv. "It is a really important game for us, and we must gain points.
"We know against top teams anything can happen but we need to be strong enough to go into these games with confidence.
"Or course playing in Old Trafford is really difficult but we have to believe that we can go and win also. And if we keep doing our job as we are, we will be much closer at the end of the season."
He added: "When you get good results, the team starts to believe a bit more. We are in the quarter-finals of the Champions League again and it is really important for the confidence.
"But to be in it next season we have to finish fourth so we cannot forget the Premier League. We need to keep working harder in both competitions."