Moyes has spent almost 11 years with the Toffeemen and is widely regarded as one of the best managers in the Barclays Premier League.
But his contract is due to expire in the summer and the Scot has been linked with a host of top jobs, including Manchester United when Ferguson eventually decides to call it a day.
Understandably, Everton chairman Bill Kenwright is keen to keep Moyes on Merseyside, and the chances are, in the short-term at least, that is where the Scot will stay.
However, after spending so many years punching above their weight, Ferguson feels Everton may be in trouble should Moyes walk away.
"It's obviously a concern for Everton," said Ferguson.
"It would be a big blow because he's a good quality manager."
Yet again this term, Moyes has shoved Everton up the table, ahead of Arsenal and Liverpool, and they are presently only three points adrift of fourth-placed Tottenham.
Last time Everton qualified for the Champions League though, they failed to reach the group phase, part of a frustrating sequence of results in key matches that has stunted their progress.
Not that Ferguson views it has having any effect on Moyes' CV.
"He's had 10 years at Everton - you don't survive 10 years in this game without making progress," he said.
"His ability is obvious.
"Whether he gets in the top four doesn't change my opinion of him, or anyone else's."
The bond between Ferguson and Moyes is strong.
Yet it was the 4-4 draw with Everton last season - the visitors rallying from 4-2 down with eight minutes to go - which arguably cost United a record 20th title and opened the door for Manchester City.
Then, at the start of this season, Marouane Fellaini scored the only goal at Goodison Park to put Everton in with a shot of their first league double over United since 1969.
"They have a genuine chance of being in the top four," said Ferguson.
"The title race is between ourselves and City, but after that you've got Chelsea, Tottenham, Arsenal, Everton and even Liverpool, who are starting to get more consistency after that result last weekend.
"But Everton are there on merit.
"They are a difficult opponent. They have only lost three games, so they are obviously hard to beat.
"And that's in the mould of David Moyes.
"He's made gradual progress because when he first took over he didn't have any money to spend.
"Given time you can do these things, which is the great value Everton have got out of David - each year he has progressed to good levels."
The memory of Everton's visit last term is seared into Ferguson's mind.
Twice United gained a position of comfort, only to toss it away in almost reckless fashion.
The issue has not entirely been addressed judging by the number of times the Red Devils have ended up hanging on this season in matches that appeared to be won.
Yet Ferguson feels a fundamental point has been rammed home.
"It is about anticipating the unexpected," he said.
"We didn't do that against Everton, after being 4-2 up with eight minutes to go, it definitely cost us the league.
"If we are 4-2 up with seven minutes to go this time it won't happen again."
Ferguson's options have been bolstered by the return of Ashley Young from a five-match absence with a knee injury.
In addition, Phil Jones and Michael Carrick have recovered from the bout of shingles and hip problem respectively that kept them out of international duty in midweek.