The Premier League champions are languishing in seventh place in the table, 18 points behind leaders Chelsea and 12 behind Arsenal who occupy the final Champions League qualifying spot.
"If Sir Alex was here it would be difficult for him as well," Moyes told British newspapers. "It could have been the case no matter what, this season.
"It has been so un-Man United which is why we have to look to continue a policy of building, improving, getting better."
Moyes has been heavily criticised since arriving in the close season from Everton.
United won 13 Premier League titles under Ferguson before he ended his 26-year reign at Old Trafford by retiring.
"People are aware there is a squad that is ageing so I think it would have been a tough season for whoever was in charge of Manchester United this year," said Moyes ahead of the lunchtime kickoff with Aston Villa at Old Trafford.