David Moyes has taken a lot of the blame for Manchester United's struggles this season, but he believes Sir Alex Ferguson would have also found it challenging to win with the current squad at Old Trafford.
Moyes said any manager -- including Ferguson -- would have found it difficult to win a title with United's ageing roster.
United's squad includes quite a few players over 30, including centre-backs Nemanja Vidic and Rio Ferdinand, left-back Patrice Evra, midfielders Ryan Giggs and Michael Carrick, and striker Robin van Persie.
"People are aware there is a squad that is a bit more ageing, so I think it would have been a tough season for whoever was in charge of Manchester United this year," Moyes told national newspapers.
"And I actually think if Sir Alex was here this year it would be difficult for Sir Alex as well and I'm sure he would be aware of it."
United are 18 points adrift in seventh place entering this weekend's fixtures, but Moyes said he's aware that Manchester United does not have the luxury to have a down season like many smaller clubs.
"It could have been the case no matter what this season, but it has been so un-Man United, which is why we have to look to continue a policy of building, improving, getting better and that's what we'll try and do."
Earlier this week, blame for United's season spread to Ferguson as well, with fans yelling at the former manager after a 3-0 defeat to Manchester City.
Chelsea manager Jose Mourinho said he cannot comprehend why some supporters would blame Ferguson for the club's struggles this season.
"Lots of people are speaking about Sir Alex. He made Man United what Man United are," Mourinho said. "He decided to retire. When somebody decides to retire, especially a person like him, he deserves to retire. He deserves to enjoy his life.
"And now he's responsible for what? Man United lose a match, it's his responsibility? Man United struggling in the Premier League is his problem?
"(Wayne) Rooney misses a goal, it's his fault? Or (David) de Gea makes a mistake and it's his fault?
"He can only be blamed for one thing: Man United being the club Man United are. He's retired. Let him retire in peace."
Mourinho said Moyes can still salvage United's season by winning the Champions League.
"Why are we speaking about failure, failure, failure? Let him finish the season. If he wins the Champions League..."