The midfielder says the support of his family plus his determination and success with the Belgium national side helped him maintain his mental strength even when things were going badly for him and the club.
Fellaini was ex-United boss David Moyes' only signing of the 2013 summer transfer window for £27.5million from Everton,
The 26-year-old however failed to score in his first season at the club and rarely performed to the levels he had shown under Moyes at Everton, but has found his feet under Louis van Gaal with some impressive performances.
Asked if felt he was made a scapegoat last season, Fellaini said: "Yes a little bit
That is a difficult question
It is difficult to answer that."
Speaking at an event organised by Manchester United's global partner Nissin, he added: "I didn't lose faith in myself
In football you have to be strong in the head
The mentality is important and I do have this quality so I can keep going.
"My family helped me through it
I was also in the national team for Belgium at the World Cup and I played well and the team also played well
For my confidence that was important
I came back after the summer confident.
"The manager said to me I would have to fight if I wanted to play
I did fight and trained hard and that was it
When I got my chance I tried to show myself and tried to do my best.
"Last season was a difficult season for me
The World Cup helped me a lot
The manager of the national team and the players helped me and it was a great experience for everybody."
Fellaini said his current form is partly the result of recovering his fitness after an ankle injury - but that there is more to come.
He said: "When you are playing you are always happy
So I am happy at the moment
I have worked hard and will work hard to play every game.
"I am fit now and that is why I am better
When I am super fit I will be better I am sure
I was injured earlier this season, they said I had to have surgery but I didn't
It was a bad injury but now I am better and I can look forward.
"At the moment the manager is using me as a box-to-box player and I am trying to score a goal."
Fellaini said Van Gaal has brought in a different approach to Moyes which the players had to get used to.
He added: "I agree last season was tough
There was a new manager and it was difficult for all the players but we have another new manager now with a new philosophy and we have to work hard.
"It is about organisation and keeping the ball better
You have to close down when you lose the ball
It is a new philosophy.
"When you bring in a new manager you have to wait because it is not easy to bring in a new philosophy but we are working hard in training
The manager has a lot of meetings to help us improve so we will see what happens in time."
:: Marouane Fellaini was speaking at the screening of 'HUNGRY TO WIN' a Japanese animation created by Nissin, Manchester United's Official Global Noodle Partner.
Source : PA
Source: PA