Blues’ Portuguese defender said: “The performances of Didi and Cristiano will decide the destiny of the title.
“My two friends are having unbelievable seasons and there is more to come from them both.
“I believe it is still possible for Chelsea to win the title.
“There are still a great many matches to play and there could be some bad results for United in the coming weeks.
“Drogba is a key player for us. Chelsea always need his goals and, in my view, he is a more motivated striker now than he’s ever been while he has been at this club.
“Is this state of mind he can be the person who will be the most decisive in our season.
“But I know Cristiano well and his objective is to be the top scorer in Premier League. If he can do that he will be the key to United’s success.”