Manchester United boss Sir Alex Ferguson says it would be wrong to dismiss Chelsea's chances of winning the Premier League this season.
United, along with locals rivals Manchester City, hold a 100% record after four games and meet Chelsea at Old Trafford on Sunday.
“Chelsea will also want to test United's defenders and see how they react collectively because the season has been a cruise so far. It will be difficult but, if Chelsea can do that, they have got a chance. In no way is it a foregone conclusion United will win this game because the London club have too many good players.”
"Chelsea will be there at the end of the season," Ferguson said.
"The Manchester teams are enjoying the publicity but Chelsea are lurking and will enjoy not being in the spotlight."
The Blues have made an unbeaten start to the campaign and lie third in the table, two points behind United and City.
United beat Chelsea 2-1 in the corresponding fixture last season, but in 18 Premier League matches at Old Trafford, United have won six, Chelsea have won five and there have been seven draws.
Ferguson expects another tight encounter at the weekend.
"It will be a fantastic game," Ferguson said.
"The games between both sides over the last seven years have been very close affairs.
"There is usually just one goal in it and it will be very tight on Sunday again."
Ferguson, who celebrates his 70th birthday on 31 December, will face new Chelsea manager Andre Villas-Boas, who is 36 years his junior.
Manchester United manager Sir Alex Ferguson
“The games between both sides over the last seven years have been very close affairs”
The Scot said he was impressed with the start his Portuguese counterpart has made at Stamford Bridge.
"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.
"They are a team with great experience and they will always be a challenge to us."