"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.