The former United striker admits he still watches the Premier League.
Forlan said: “Chelsea have more quality, are more experienced and are a much bigger threat than they were in my time at United.
“They lost at the weekend, but, for me, they are the best team in the Premier League. With the arrival of Ancelotti, he has made them stronger in defence and more dangerous going forward.
“Ancelotti has really motivated players like Drogba, Ballack and Anelka. The absence of Drogba for the Champions League makes it difficult for them and is good for us.
“But we are prepared for Stamford Bridge and we know we can cause an upset and hopefully I can score. I always get a reaction from the English supporters but that only inspires me.”
Atletico faces Chelsea at Stamford Bridge in the Champions League on Wednesday.
Forlan added: “Every time I play an English club in the Champions League, after my time at Manchester United, I feel it’s like a personal vindication for me.
“After the defeat against Argentina, it would be beautiful for me to win in London and this game could be decisive for us.
“Atletico Madrid are not playing well in La Liga and we know that this game is so important for us in the Champions League.”
