Sir Alex Ferguson has a theory about why Roy Keane will not become a top manager

"He went ‘Wrong. There is something not right there’."

They haven't worked together in 12 years, but the working relationship between Sir Alex Ferguson and Roy Keane continues to provoke interest. The former Manchester United manager and his captain forged one of the most successful partnerships in British football history, winning seven league titles, four FA Cups and the Champions League together. Keane was Ferguson's most important player during the Irishman's 12 years at Old Trafford, the driving force behind the team's success and the best midfielder of his generation. There were more naturally talented players than Keane, but few more determined, intelligent, and reliable. No matter what the on-field situation, Keane took responsibility and gave his all for United. Ferguson once said:

"If I was putting Roy Keane out there to represent Manchester United on a one against one, we'd win the Derby, the National, the Boat Race and anything else. It's an incredible thing he's got."

However, Keane's bitter departure in 2005 caused a rift between the men that has never been repaired. The former United captain criticised some of his teammates in an interview, and it led to an explosive showdown with Ferguson in a team meeting. They have taken shots at each other in their autobiographies in the past few years. Keane is also one of the few former Ferguson players not to attend club events, such as the unveiling of a statue for the Scot at Old Trafford, and it seems unlikely that they'll ever be back on friendly terms. Keane was Ferguson's most important player, and the foundation of their working relationship had appeared rock solid. It seemed as though they had won too much together, and shared too many similar values, to fall out. Keane was even spoke of as a potential successor to Ferguson at Old Trafford. However, just as their relationship didn't pan out as expected, Keane's spell in the dugout has not gone according to plan. It began brilliantly. Keane took Sunderland from the relegation places of the Championship to the Premier League and kept them there. He left in December 2008, but, given Sunderland's struggles since then, it can be argued that Keane did a decent job at the Stadium of Light. He then became Ipswich Town manager, but was sacked in in January 2011 after failing to make an impact at the Championship club. He has been assistant manager to Martin O'Neill with the Republic of Ireland since 2013. There's still time for Keane to become a good club manager. But, even if he doesn't, he is by no means the first great footballer who found it difficult in management. It appears Ferguson didn't fancy his chances in the dugout from the beginning. According to Alastair Campbell, who served as communications chief to former Labour Prime Minister Tony Blair, Ferguson disregarded Keane's potential to become a good manager in September 2006, just month after the Irishman became Sunderland manager. The Scot claimed that Keane "didn't like people" and this would hold him back in management. Campbell writes in his diaries covering 2005 to 2007 that, Ferguson:

"...felt he had what it took in so many ways, but he had demons and they would come out. He was actually someone who didn't like people that much unless they met his own standards."

Campbell, who is a friend of Ferguson, expressed surprise when Keane left United in 2005.

"I said you used to say he was the most intelligent player you'd had, and the one likeliest to be a top manager. He (Ferguson) went 'Wrong. There is something not right there'."

Campbell is also friends with former Liverpool and Tottenham Hotspur midfielder Jamie Redknapp, who told him that Keane "probably had too big an ego to be a manager". This was before the Irishman took his first job in management. In his second autobiography, Ferguson was equally disparaging of Keane's ability as a manager, writing:

"As his career in coaching developed, it became apparent that he needed to spend money to achieve results. He was always looking to buy players. I didn't feel Roy had the patience to build a team."

That seems a harsh assessment by Ferguson, considering every manager needs money to build a squad. But it serves as further evidence of the rift between the pair.