Chelsea's ability to grind out victories will make it very difficult for anyone to catch them in the Premier League, Manchester United manager Jose Mourinho has said.
United, unbeaten in their last eight league games since being thrashed 4-0 at Stamford Bridge, are sixth with 30 points after 17 matches.
They are 13 points behind leaders Chelsea, who are six clear of second-placed Liverpool.
"You have to be honest and say that is very difficult. It's not just the difference in points, it's also the Chelsea philosophy of playing," he told British media about his side's title chances.
"They score one goal and they win. They defend a lot. They defend well ... 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."
United have narrowed the gap to fourth-placed Arsenal to four points thanks to three straight wins, and Mourinho was reluctant to predict where his side might finish.
"Let's see where we finish. I don't want to say fourth, because I think we can do better than fourth," he added.
"But we have the risk of not finishing 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."
United host 18th placed Sunderland on Boxing Day while Chelsea play Bournemouth.
Elsewhere Arsenal play West Bromwich Albion and Manchester City play Hull.
Liverpool play Stoke on Wednesday morning and Tottenham play Southampton on Thursday morning.