It is never easy to replace a legend, and at Manchester United Roy Keane was certainly a legend. Signed for £3.75million, a then British record, Keane won seven league titles, four FA Cups and a Champions League, and was instrumental in their treble winning season in 1999. His performance in the second leg of the semi final against Juventus, having already picked up a booking that ruled him out of the final, is thought to be the key factor in United coming from two goals down to win 3-2. Given all that Keane brought to the club, it is strange Sir Alex Ferguson has never properly replaced him. Of course, its not been for a want of trying and it is fair to say that since the era of Keane, Vieira and then Makelele, many Premiership teams have failed to find that midfield general, the combative leader who gets going when the going gets tough. However, United have missed their general more than most and the question has to be asked has it cost them? Since the Cork-born midfielders departure to Celtic in November 2005, United have won four league titles, a Champions League and two League Cups, so the first thought is no, they havent missed Keane or a player of his ilk. But delve deeper and you find the Old Trafford trophy cabinet could be filled with even more cups and titles. Last season the Red Devils lost on goal difference to local rivals Manchester City. They have lost two Champions League finals to Barcelona, while the last European campaign was horrific. The capitulations to FC Basel (twice) and Benfica at Old Trafford are prime examples of what is wrong with the team, while Athletic Bilbao ran through an exposed United at will. Going forward Fergies men are, at times, irresistible. The movement of Hernandez, the finishing of Welbeck, the power of Rooney, the trickery of Nani and Young, they can score against anyone, and score often. The defence is impressive as well. After a tough start David De Gea is starting to look world class, Nemanja Vidic was badly missed but Jonny Evans improved his game, Chris Smalling and Phil Jones have potential, and Rio Ferdinand had people clamouring for an England recall that sadly did not arrive. While the full backs were at times suspect there is potential in Rafael, and Patrice Evra has the experience to bounce back. The problem is in midfield, and specifically the heart of midfield. The loss of Darren Fletchers drive and determination was a blow, but even when the Scotland captain has been fit there was always something missing. The way Xavi and Iniesta exposed United in both Champions League finals showed that they missed an international class defensive midfielder, someone who could protect the back four, break up play, and close down the space the likes of Messi and Iniesta love to roam in. Michael Carrick, while attractive on the ball, lacks the steel to battle with superior opponents, Anderson may literally be a man mountain given the weight he has put on but he certainly does not look like the rock you could build a midfield on, while Eric Djemba-Djemba and Kleberson were not fit to wear the red shirt. The signing of Owen Hargreaves for £17million shows Ferguson knows what his side need, and if it were not for Hargreaves horrific injuries who knows how much the ex-England international would have improved United. The fact that Ferguson has not re-entered the market for a defensive midfielder is disconcerting for the Old Trafford faithful. It is an issue that everyone seems to be aware of, and while Shinji Kagawa is an effective replacement for Paul Scholes, Ashley Young has taken Ryan Giggs left wing spot, and first Cristiano Ronaldo and now Nani have taken David Beckhams position on the right, there is no replacement for the acerbic ex-captain Keane. Links to Javi Martinez, Yann Mvilla, and Lucas Biglia may just be wishful thinking on the part of fans and journalists. Ferguson has ruled out moving for a holding midfielder, stating on Uniteds official website that he his has never selected one in his life. While you can argue that Keane was much more than just a holding midfielder, his defensive qualities have never been replaced, and given the move from 4-4-2 to a three-man central midfield, especially in Europe, perhaps it is time Ferguson adjusted his thinking. Drive, determination, aggression, bite in the tackle, leadership those are Keanes qualities that United miss the most. Nothing but your best was acceptable, and if your best was not good enough, you did not deserve to be a Red Devil. With the spending power of their rivals, not just in England but across Europe, there is a danger Manchester United may start to slip behind. Unless they address the last weakness in their team, the ghost of Roy Keane will haunt Manchester United.