Manchester United boss Sir Alex Ferguson says Chelsea remain their biggest title rivals.

Despite the regular threat of Arsenal and the ambition of Manchester City, Ferguson feels it is the reigning champions who are their main rivals this term.

"The Premier League is such a difficult league, it's almost tribalism and you can't dismiss that impact when it comes to winning the Premier League," the Scot told CNN International.

"I always look at the team that wins the league the year before, you have to have a target to try to work on.

"It's up to the rest, including us, to do that and Chelsea are the champions. They've had a good start to the season and I look upon them as the main danger to us.

"The games that will matter will probably be the ones against each other. Last year we lost both of those games and therefore that decided the title."