Sir Alex Ferguson has voiced his support for Manchester United's defenders in the light of a relatively disappointing start to the season by the reigning Premier League champions.

United, who set a world record of 1,311 consecutive minutes without conceding a goal last season, have been far more susceptible this term, allowing 11 goals in as many Premier League games.

More worryingly, United have leaked seven goals at home, more than clubs in or around the relegation zone such as Birmingham, Hull and Wolves.

Ferguson's team has not been aided by the absence of Dutch international goalkeeper Edwin van der Sar, who was in goal during last season's record-breaking run and injuries to Nemanja Vidic and Rio Ferdinand.

Those circumstances have forced the United manager to name 16 different defensive line-ups so far this season.

However, despite the lack of continuity in his defence and the loss of form of key personnel such as Ferdinand, Ferguson insists United's defensive frailties are not a cause for concern ahead of Sunday's clash with table-toppers Chelsea, two points in front of the Scot's side.

"Changing defensive line-ups didn't affect us last year," said Ferguson. "When we were on that run of 12 clean sheets we were changing the back four all the time so the players are there. We are lucky, we've got a good squad so I don't see why that should be the problem.

"But I think you also have to look at the number of goals scored in the Premier League this season as opposed to the previous season.

"It's the most there's been so maybe we are just in one of these unusual seasons, but it would be nice to get clean sheets - no question about that," he added. "It makes a difference."

Coincidentally, United's record run of a dozen Premier League games without conceding a goal started last season following this corresponding weekend and Ferguson believes that, contrary to the current form book which includes Tuesday's 3-3 home draw with CSKA Moscow in the Champions League, his team is capable of repeating that feat.

"It's a team of great ability," said Ferguson. "Maybe the strongest part is that we've got some variations to counter-act the injuries we get.

"We've got Wes Brown and Jonny Evans, last week they were tremendous against Blackburn and strangely enough on Tuesday Jonny was magnificent, particularly in the second half.

"Although they scored three goals, I find it hard to fault my central defenders. I just think we were too open.

"I just think we had a challenge last year and they accepted it. The challenge was we had to go to Japan (for the World Club Championship) and that focused all of our minds.

"We needed to get results before we went to Japan and after we got back because we were going to be games and points behind teams. They buckled down to the job and it was a fantastic job from them.

"The challenge now is to win the league. Someone made the point the other day, I don't think the Premier League settles until the internationals are over. Once we go over this next bout of internationals and the league settles down, we will probably see a truer league."