Keane's tenure as Sunderland manager came to an end on Thursday
Manchester United manager Sir Alex Ferguson is uncertain whether Roy Keane will return to football management.
Keane resigned as Sunderland manager on Thursday after 27 months in charge of the Black Cats and his future in the game remains unclear.
"It is difficult to say whether he will be back," said Ferguson.
"He is an incredibly controversial character. Every week he always had something to say about the game. He was the same as a player."
Ferguson, who Keane played under at Manchester United, added: "He is such an interesting character and did a decent job up there."
Keane, who had spent more than £70m on 33 players since 2006, guided the club into the Premier League during his first season as manager before keeping them there last term.
And despite recent results, which have seen Sunderland win just one of their past seven games, the Black Cats are still in a better position this year than they were at the same stage at last season.
Former team-mate and now Manchester City boss Mark Hughes believes Keane's exit may have come as a result of not taking a decent break between finishing his playing career and taking over as manager at a club.
The 37-year-old Irishman went to Sunderland in August 2006 almost immediately after injury finished his playing career at Celtic in June of the same year.
Hughes also began his managerial career immediately but believes he was helped by the fact that his first role was as Wales boss, with the intermittent nature of the international calendar giving him time away from the game.
"You sensed in recent weeks that maybe there was a point where he was going to consider his future and walk away," said Hughes.
"He is still young and still has a future in the game, if he wants to return there is plenty of time for him to do so.
"Maybe he went from being a player to a manager too quickly.
"I think it is important to have a bit of breathing space once you stop playing and although I went straight into management it was with Wales so I still had a bit of time off. I don't think Roy had that benefit.
"He needs to take a step back, learn from the experience and go again."
Keane can return to management - Dunphy
However, Ferguson believes the problem is more deep rooted than that, with the pressures of management taking a greater toll than ever.
"There are very few managers that last more than three to four years at a club nowadays and the lifespan of a manager at a club is getting shorter and shorter," he said.
"They can move on to different challenges, but it's a very precarious industry nowadays and a very emotional game.
"A couple of years ago, people were saying that I should have gone four years earlier - the black flags were out!
"Football people like myself are fortunate to have been at a club for so long, though. I haven't had to go through that emotional situation."
Arsenal manager Arsene Wenger expressed his surprise at Keane's resignation but believes he will make a return to management.
"It is a surprise, but I can understand it," said Wenger. "He is a passionate man, and I regret he leaves the job.
"When you are passionate, especially at the start of this career, you suffer immensely physically. Also, because he is a passionate man, there is no other way for him to be in the job.
"When you are passionate about the game, you go out of it and then come back into it because there is no other way to be happy. That is why I believe he will be back."
Ince fumes at 'bang out of order' media
Another of Keane's former team-mates Paul Ince has urged for young managers to be given more time while also backing him to return to the game.
Ince himself is under pressure at Blackburn where his side have made a bad start to the season.
"He'll be back. He is a fantastic manager, but we've lost him now," said Ince.
"I've said it before, managers need time, just look at Sir Alex Ferguson.
"You can't just keep sacking young managers and putting them under pressure. We need to be backed."
Gary Pallister is another of Keane's former team-mates who like Hughes believes the Irishman needs a break from the sport.
"I think Mark Hughes made a very good point that he's never had a rest from football," Pallister told BBC Sport.
"He finished playing and went straight into management so I think he will enjoy a rest with his wife and his kids and recharge his batteries.
He is a very different type of character and is pure box office, he speaks from his heart and he is very blunt in his assessment of things
"It's very hard to second guess Roy he is very much his own man and he might decide that he is not comfortable being a manager but then he might decide he misses it."
Pallister added: "Can he find something else to occupy his mind or will he miss football that much he wants to get back into it?
"I'm not sure even he will even know - he needs a break to clearly focus on what he wants to do."
Pallister also admits that he would not be surprised if Keane left football for good.
"I honestly think he needs time to walk away and look at the bigger picture," said Pallister.
"He has a big family back in Manchester and he will look at his options and see if he wants to go back in the madhouse as Fergie (Sir Alex Ferguson) called it.
"He is a very different type of character and is pure box office, he speaks from his heart and he is very blunt in his assessment of things.
"It would be a worse footballing world without him in it because he is one of the characters that make you sit up and take notice."
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