Manchester United manager Sir Alex Ferguson has said that Chelsea are still one of United's biggest challengers for the Premier League title.

United and local rivals Man City are the only two clubs with a perfect 100% start to the season but Ferguson thinks that Chelsea will enjoy being just in behind them.

"The Manchester teams are enjoying the publicity but Chelsea are lurking and will enjoy not being in the spotlight," he said.

The Scot has also praised new Blues boss Andre Villas-Boas, who is 36 years his junior, ahead of their Premier League encounter on Sunday.

"For a young man who has come to Chelsea, it is a great challenge," he added.

"It is a hard challenge at his age but when you go to a new club, you hope you get an immediate response. He has got that."

In the last seven seasons United and Chelsea have been the only clubs to win the Premier League - United four times, Chelsea three.