"Whenever the day comes, he'll be a big loss of course, but I won't be concerned about that until it actually happens," Ferdinand told The Sun.
"All I'm thinking about is what a great manager we have with us now - not about what's going to happen two or three years down the line.
"I won't be worrying about him leaving at all next season and I don't suppose the rest of the lads will be either.
"We will be talking about what we can achieve with the manager we've got.
"He's the best manager ever at a British club. He's won everything there is to win and is almost irreplaceable.
"When someone has to fill his shoes that person is going to have a massive job.
"But the boss has put such good foundations in place that I don't see why United should fall apart when he goes.
"The club will be preparing for it. It's not like he's going to get up and leave tomorrow. Things will be looked after properly.
"The boss has too much love for the club to just leave it in the lurch so I think it will be a smooth transition."