The Blues can knock Arsenal out of the title race with a victory int he clash.
“Arsenal have a good squad but this season have failed in the big matches against United and us,” he told The Sun.
“That is the key when it comes to fighting for the title and perhaps the pressure and the anxiety of it all is damaging Arsenal’s performance at decisive moments.
“Sunday’s match is so important. It is certain that defeat for Arsenal will eliminate them as a rival for the title.
“If Arsenal are nine points behind us it’s not just a matter of that distance but the question of morale.
“If we beat them again they will have to think about two defeats against us and that will be a very negative situation for them. So this match is like a final for them and this extra pressure is a positive for us.”
“Injuries affect many teams and I think they have a real problem in attack where the absence of Robin van Persie has proved to be a very important factor,” said the Portuguese midfielder.
“Their young players have been sensational but they have still not exploited their chances to become champions. United, for instance, have more experience and that is what matters at this stage of the season.
“So it is normal that the race is between United and Chelsea. Predictions made in the summer are being fulfilled.”
