Moyes' men are struggling in seventh in the Premier League, with the Scot under increasing pressure after poor losses to rivals Liverpool and Manchester City.
Replacing Ferguson was always going to be a tough task for Moyes, who said even the man who led United to 13 league titles – including last season – would have found it hard this season.
"I actually think if Sir Alex was here this year it would be difficult for Sir Alex as well, and I'm sure he'd be aware of it," Moyes said.
"I think people are aware there's a squad that is a bit more ageing, so I think it would have been a tough season for probably whoever was in charge of Manchester United this year."
Reports in the British press have suggested a group of fans are set to fly an aeroplane sporting an anti-Moyes message over Old Trafford ahead of Saturday's clash against Aston Villa.
Moyes believes he has the support of the fans, who he praised for their understanding during major change.
"The supporters I see are the ones I speak to, and I have got to say the supporters outside Old Trafford have been fantastic," he said.
"I would say United supporters have probably been as good as people have seen them for many a year because they understand there is a change.
"There has been a change from a great manager and not just a great manager, but a manager who was here for 25 years, and to make that change is always going to be difficult."
