Manchester United boss Sir Alex Ferguson insists his side will produce a better performance against Chelsea than they did at Liverpool.

United lost 2-0 at Anfield last month but now as the Premier League's two leading sides prepare to clash at Stamford Bridge on Sunday, Ferguson insists his players will be prepared.

"It's always hard at Chelsea but we'll deal with it better than we did at Anfield," said Ferguson.

"It was difficult at Anfield. You have to have a winning mentality and it was missing at Liverpool.

"Players are human so that can happen."

Meanwhile, Gary Neville admits the constant changing defence has been an issue this season.

John O'Shea looks set to come in for the suspended Neville on Sunday, whilst Rio Ferdinand is still sidelined with his calf problem.

"We are interchanging the defence too regularly at the moment because of injuries and it has caused us a problem," he said.

"We had to change our keeper for the opening two months of the season, then Rio Ferdinand and Nemanja Vidic have been injured. Before that it was Wes Brown.

"It means more changes than a manager would like.

"He wants a consistent back four, which is what we have had for two or three seasons.

"We definitely want to improve defensively and once we settle into our stride I am sure we will become better."

One boost for Ferguson is Antonio Valencia, who he feels is starting to hit his stride following a £17million summer switch from Wigan.

"It is good to see him scoring," said Ferguson.

"He did not show a scoring ability when he was at Wigan but when he came to us we talked about this and the fact if he is to progress his career, it was something he should work on.

"He is showing evidence of progress now.

"He has settled in and is emerging as a top performer.

"He has strength, good balance, speed and is a good crosser of the ball.

"But the main thing is that he is now playing with much more confidence.

"I am delighted with his steady improvement and hopefully he will prove to be another valuable source of goals as we move through the season."