Roy Keane believes Sir Alex Ferguson is still trying to exert "control and power" at Manchester United despite retiring as manager in the summer.
The Irishman, who was Ferguson's midfield driving force in a glorious spell for the club between 1993 and 2005, says the Scot has a "massive ego" and rated his former boss at Nottingham Forest, Brian Clough, as the best manager he had worked with.
United have endured a difficult start to life under Ferguson's successor David Moyes, having lost three Premier League games at Old Trafford already this season to sit ninth in the table.
Keane said of Ferguson, now a director at United: "Everything is about control and power. He's still striving for it now even though he's not manager. There's massive ego involved in that."
Keane, who left United in 2005 after a fall-out with Ferguson, was speaking in a new ITV4 documentary called 'Keane and Vieira: Best of Enemies' (which airs on Tuesday at 10pm), which is about his rivalry with former Arsenal captain Patrick Vieira.
He said that his relationship with the former United boss is now "non-existent".
The Irishman also took issue with Ferguson praising him in his recently released autobiography for "covering every blade of grass" in the 1999 Champions League semi-final second leg against Juventus.
Keane added: "Stuff like that almost insults me. I get offended when people give quotes like that about me. It's like praising the postman for delivering letters."
Keane admitted he had cried in his car when his United career came to an abrupt end over a candid interview he gave to the club's in-house television station criticising his team-mates.
He said: "Of course I was upset: I did shed a few tears in my car for about two minutes.
"But I also told myself I had to get on with my life.
"I walked out with nothing, I had no club lined up and I was injured.
"I told David Gill I had been injured playing for Man United.
"I could have played for Manchester United easily for another couple of years."
Keane said Ferguson's strongest trait was his "ruthlessness", while labelling "loyalty" his biggest weakness.
And now Ferguson has retired, Keane revealed he and his son have season tickets at Old Trafford.