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 an ITV4 documentary and said that his relationship with the former United boss is now "non existent".
The Irishman even 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 laughed off the furore surrounding the infamous MUTV interview and said he felt the row between Ferguson and then club director John Magnier over the stud rights to racehorse Rock of Gibraltar had to have had a "negative effect" on the club.
Keane said: "I managed the dressing room: that was my job.
"If people didn't think (the Rock of Gibraltar row) had a negative effect on the club, then they are in cuckoo land."
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.
Ferguson said in his autobiography that his authority at Old Trafford would have been undermined had he not forced Keane out in 2005.
The Scot said Keane had "slaughtered" several of his team-mates in the MUTV interview. Ferguson said Keane invited the United players to watch the interview, but that the decision backfired when several senior players, including Dutch duo Edwin van der Sar and Ruud van Nistelrooy, rounded on the captain.
Ferguson said at a press conference promoting the release of his book in October: "'We had to react to the situation so quickly because his actions were so quick. For one reason or another, he decides to go and criticise his team-mates.
"Most of you won't have seen the video but you couldn't release it. You just couldn't.
"It ended up with two of our young players being booed before a Champions League match in Paris because of it.
"We decided we had to do something. The meeting in the room was horrendous. I just couldn't lose my control in this situation.
"If I had let it pass and allowed it to happen, the players would have viewed me differently. Much more differently to how I would have liked to have been judged.
"Throughout my career, I have been strong enough to deal with important issues like that. Roy overstepped his mark. There was no other thing we could do."
Responding to the comments about him in Ferguson's book, Keane told ITV in October: "I do remember having conversations with the manager when I was at the club about loyalty and, in my opinion, I don't think he knows the meaning of the word."