Sir Alex Ferguson has claimed that the current Chelsea side is not the strongest he has faced.

Chelsea are unbeaten at the top of the Premier League and are current European champions, but Ferguson thinks that they lack the 'ruthlessness' of the Jose Mourinho era.

"I wouldn't say this is the strongest Chelsea team," he said. "If you go back a few years to that period of [Didier] Drogba, they were really formindable, difficult to play against.

"[John] Terry was younger, [Frank] Lampard got 30 goals from midfield one year, we'll never see that again. They were a really powerful team, hard to beat and ruthless.

"When I first saw them playing Oscar, [Juan] Mata and [Eden] Hazard in the same team I thought it was a risk. If you can contain the three in the middle of the park then you've got a chance."

United play Chelsea at Stamford Bridge at 4pm this afternoon.