Ferguson celebrated 25 years in the United hotseat on Sunday.

As Ferguson has shown no inclination to surrender his position, the search for a successor has yet to begin.

However, when it does, Gill has highlighted some non-negotiable requirements the new man must meet.

"It will be difficult to replace him - it's naive to say anything other than that," Gill told MUTV.

"But we are a great club whose values go back in history to our heritage to the 50s and 60s and the last 25 years with Alex.

"To continue with that, the new manager needs to understand those values and the vision for the club and must buy into that."

As he approaches his 70th birthday on New Year's Eve, no-one could accuse Ferguson of concentrating on his immediate priority of withstanding the challenge posed by Manchester City at the expense of United's future.

In Phil Jones, Chris Smalling, Danny Welbeck and Tom Cleverley, Ferguson has integrated a quartet of young English players to his squad this season that could provide a platform for United over the next decade.

It maintains a philosophy Matt Busby introduced to Old Trafford with his famous 'Babes' back in the 1950s and which Ferguson quickly recognised needed to be revived after he succeeded Ron Atkinson in 1986.

"I believe in young people," Ferguson told Sirius XM.

"You need a foundation at a football club and that is vital. You can build a first team, but you really do need the back-up and the foundation to make it a football club."

Ferguson will forever be remembered for bringing through the famed 'Class of 92'.

However, he takes just as much pride in the elevation of Cristiano Ronaldo to world player of the year given he was just a raw teenager when he first arrived from Sporting Lisbon in 2003.

"With all the young players that come to us in their formative years, you have got a job to make them good footballers but also to show them how to grow up the right way," he said.

"Cristiano came to us at 18, just a young lad from Portugal who didn't know the country.

"But he learned the language, adapted very well and he has turned out fantastically as a human being, just as was the case with the Nevilles, Scholes, Beckham, Giggs and all those lads."

Ronaldo eventually left for Real Madrid in 2009 for a world record £80million.

He has never forgotten the effect Ferguson had on his career though, just another example of how the Scot's influence at United goes far beyond the 12 Premier League titles and two Champions Leagues that form the basis of his staggering trophy haul.

"Alex's legacy to United is to my mind very clear - delivering an unprecedented period of success in the Manchester United way," Gill said.

"By that, I mean attractive football using young players - both homegrown and buying players when necessary like Ronaldo and Rooney, but actually developing our own players.

"That record is there for everyone to see and that legacy is very clear also.

"Within that, he's made sure he's cemented United's position as one of the top clubs in world football.

"We're very well respected clearly in this country and around the world, you only have to see our following there on tour in America and Asia, plus in Europe when you speak to any other club.

"United are rightly held in very high esteem down in no small measure to what Alex has achieved in the last 25 years."