Manchester United boss Sir Alex Ferguson has admitted he is concerned about Arsenal's style of play ahead of the Gunners trip to Old Trafford on Monday.
The Gunners are now the league leaders after seeing off Fulham last weekend, while United's game at Blackpool was called off due to a frozen pitch.
The Scot feels the north London team have become more aggressive and mature in their approach and feels this has helped them improve in their play; they are now able to combine their slick passing with a more physical edge.
The Red Devils boss has warned they will be much harder to overcome this time round. He also added that the fixture has not become any less of a major tie since the arrival of Chelsea as title contenders.
"I think they'll still try to play the attractive football Arsene (Wenger) believes in, but there's definitely been a slight change," Ferguson told his club's official website.
"The general shape of the team has been far more mature and aggressive this year.
"They're top of the league – that's a sure indication that they are better than they were last year and they'll have a chance.
"They were very difficult to beat in the days of Emmanuel Petit and Patrick Vieira and the three at the back – Keown, Adams and Bould.
"That brought them great success and I think that this team is showing that kind of maturity now."
"The games, particularly four or five years ago, were so important because both of us were challenging for league titles."
"Chelsea have now come in and it's been ourselves and Chelsea over the last five years.
"Nonetheless, it's Manchester United against Arsenal and the history of both teams always guarantees a match of intensity and a lot of the time, controversy.
"I think Monday night's game will be more or less the same because the pride and history of both clubs determine that."
Manchester United have been boosted by the return of Rio Ferdinand who picked up a hamstring injury against Valencia midweek. Paul Scholes (groin) and Patrice Evra are both fit so are likely to play. However, Arsenal's Kieran Gibbs (ankle) and Cesc Fabregas (hamstring) are both out for the clash at Old Trafford.