Jose Mourinho says Chelsea's philosophy and strength this season will make them very hard to beat in the title race.
Mourinho says it would be very difficult for Manchester United to catch the Blues, who are top of the Premier League and 13 points ahead of his new side.
The 53-year-old was sacked by Chelsea last December after a torrid run for the then-champions, but says the way Antonio Conte has them playing at present, and the style in which they close out games, means they won't drop many points from now until May.
In an interview with Sky Sports News HQ, Mourinho said: "It's very difficult, you have to be honest and say that. Not just the difference in points, but also the Chelsea philosophy of play.
"They score one goal and they win, they defend a lot, they defend well, they are winning and in the last 20 minutes they bring defenders in, they don't care what people say, what people think, they just want to win.
"And because of that, I don't see them losing many points.
"It is mathematically possible [for United to win the league], but it is very difficult to happen for us. The difference is considerable."
United, who are four points off the top four following three straight wins, finished outside of the Champions League places under Louis van Gaal last term.
Mourinho says he does not wish to make fourth a target, insisting his side can achieve more than that despite the tough competition.
"For me to be happy, it's an accumulation of factors. For me to be happy is the way we end the season playing, the evolution of the team, the empathy with the supporters, the results in many different competitions we are playing.
"So let's see where we finish, I don't want to say fourth, because I think we can do better than fourth
"But we have the risk of not doing fourth because the competition is so hard and the top teams have the same ambitions as we have. So I don't want to say fourth or third or fifth."