A role for the club legend has been suggested following the inevitable departure of Ole Gunnar Solskjaer, but talkSPORT pundit Gabby Agbonlahor says the Irishman would instantly lose the already unstable dressing room if he arrived back at Old Trafford, as he revealed a story about his fiery tenure as assistant coach at Aston Villa.
Solskjaer is gone, with the Norwegian sacked after United's latest embarrassing result in the Premier League - a 4-1 defeat at Watford.
With a lack of top candidates currently available, and top target Zinedine Zidane reportedly not interested, the top flight giants have confirmed they are looking to appoint an interim boss until the end of the season to keep things ticking over until a new full-time coach is hired in the summer.
Former Man United stars Michael Carrick - who had a coaching role under Solskjaer - has been placed in charge for the time being, and could be given the nod for the rest of the campaign, while reports claim United legend and recently axed Newcastle boss Steve Bruce would be interested.
talkSPORT understands Mauricio Pochettino is also a target for Manchester United, and the former Tottenham boss wants the job, but it will take some convincing for Paris Saint-Germain to allow their manager - who was appointed in January - to leave.
For now, though, the club are on the hunt for a coach to come in and lift a team devoid of confidence after suffering three humiliating defeats in their last four league games.
But Agbonlahor, who was at Villa when Keane was assistant to Paul Lambert, says the former United captain is not the right man, revealing how he had no problem digging out the club's biggest stars if he wasn't happy with their performances.
Poor Joe Cole…
"The players would all be terrified, but with the way he's hammered some of them, they wouldn't play for him," the ex-Villa skipper told the talkSPORT Breakfast.
"I was with him at Villa, and he was very… how shall I describe it… angry? Ruthless?
"I remember a game, we played QPR away and Joe Cole had a bit of a cold, he wasn't his usual self, and after the game Keane hammered Cole.
"Some of the players are thinking, 'this is Joe Cole, he's a legend of the game, he's won everything', and Keane is digging into him.
"He came into the changing room and grabbed the Red Bull [Cole was drinking] and threw it across the room. He said, 'these don't work! I see you all drinking Red Bull - they don't work!'
"He's come in and done that, he's kicked the tactics board over, and we were all like, 'woah'.
"Roy lost his head, the way he was just so angry about Red Bull. And somebody said afterwards that in his book, he said he used to drink Red Bull after he played!
"We used to do a shooting drill, and Roy Keane hated it if you missed the target.
"You can probably see that now when he's doing punditry - you've got to hit the target. You've got to make the keeper work.
"So, say you're doing this shooting drill and you miss the target, all you'd hear from the side is: 'HIT THE TARGET! IT'S NOT THAT HARD! MAKE THE KEEPER WORK!'
"And we were all just like, 'urgh!' When you're doing a shooting drill you're trying to hit the corners, so sometimes you're going to hit it wide.
"The first day he came in, we did a little game of rondo and we got to seven passes or something, and he said, 'wow, is this the best it gets?' He couldn't believe it.
"He probably wasn't used to the fact we weren't the level of the Man United team he played in, we weren't as good as those players.
"We used to look over at him and he's shaking his head like, wow, this is how good you are?
"Players aren't going to respond to that. They're at their level and Roy Keane couldn't handle that our squad wasn't as good as the players he played with, that's why it didn't work and he ended up leaving."
Keane has certainly not held back in his criticism of the Man United team in recent weeks.
The likes of Harry Maguire, Fred and Luke Shaw have particularly come under heavy fire from the Irishman, who has blasted the effort of the team as a whole under Solskjaer.
He wouldn't be any different in the dressing room, says Agbonlahor, who says that style just doesn't work with modern footballers.
"That style doesn't work with the new era of players, it's totally the opposite," he said. "Maybe in Roy Keane's day that might have worked, but nowadays you're going to lose players.
"If he went into that Man United dressing room and does a similar thing, he's going to lose players. Imagine the likes of Bruno Fernandes and Luke Shaw, he's going to lose them straight away.
"I think probably Jose Mourinho is finding that now, he's losing players when he goes to clubs.
"Ole Gunnar Solskjaer is the complete other way isn't he, so you need somebody in the middle, and that's how Jurgen Klopp and Pep Guardiola are with their style - they're somewhere in between the two.
"They're ruthless when you need to be, but they'll also put their arm around you at other times. They command the respect they need but they're a good man management at the same time."