The pressure is cranking up on Louis van Gaal as a difficult campaign edges towards completion, with the Dutchman's side lagging four points behind in the race for a top-four finish.
The under-fire United boss accepts their Champions League hopes could all but be extinguished if they lose Sunday's do-or-die derby at fourth-placed Manchester City.
Thursday's Europa League exit to Liverpool means the Premier League is their only remaining route to the continent's top table - a finish Fellaini believes is the bare minimum.
"We have to do it because a team like Man United have to be in the Champions League next season," he told the BBC
"We will fight to the end to be there.
"The derby is a great sensation, (a great) atmosphere.
"All the city will watch the game - the challenge, goals, everything - because it will be a big game, so everyone likes to watch a game like that."
United supporters will not hold back if their side falter at the Etihad Stadium, if this campaign is anything to go by.
Van Gaal is not the only target of their ire as for some Fellaini is symbolic of the club's decline in recent years, with his substitution in last weekend's FA Cup quarter-final against West Ham cheered by pockets of supporters at Old Trafford.
"I think the players are used to it," he said of the criticism
"I don't read, I don't listen
I am just focusing on my job.
"Okay, sometimes it is hard for my family, but the rest I don't look at it."
It is not just Fellaini's footballing style that has been criticised as former referee Howard Webb branded him a "thug" for his physical approach in the Europa League last-16 clash with Liverpool.
In the first leg at Anfield he appeared to elbow Emre Can - though avoided any action from UEFA - and then in Thursday's return was booked for making contact with Dejan Lovren with a flailing arm.
"I don't want to elbow someone, I just defend myself," Fellaini said.
"Okay, I am physical, I like to win my challenge - that's English football as well - but I am not a dirty player."
When Webb's "thug" criticism was put to him, Fellaini added: "Yes, it's strong but I choose to defend myself, like I said.
"I like to win my challenge when I play a game
In England, it is everything with a lot of physical challenge.
"If you want to win the game, you have to be aggressive, you have to win your challenge.
"I never want to injure a player or to be bad
No, I am not like that, I just defend myself."
Fellaini will no doubt again prove a handful if selected on Sunday, when City will again be without Vincent Kompany.
The Belgium defender pulled up with his fourth calf injury of the campaign - and his 14th since joining the club in 2008 - in the opening minutes of Tuesday's Champions League clash with Dynamo Kiev at the Etihad Stadium.
"He is the captain, he gives a lot of advice to his team-mates," Fellaini said of his compatriot
"He's an important player for Man City - it's good for us.
"I feel sorry for him to be injured, you know? It's not easy when you're injured.
"I hope for him he will recover quickly and be good for City and for my country as well."
Kompany's fitness is a particular concern with Euro 2016 looming large - a tournament by when reports suggest United could well have a new manager at the helm.
Jose Mourinho's continued unemployment and desire to return to the dugout this summer has cast a shadow over Van Gaal, even if the Dutchman continues to brush questions about his future aside.
Fellaini was brought to the club by predecessor David Moyes, but appears to have affection for the man currently in charge at United.
"Of course it's easier, I knew him for five years or six years," he said about former Everton boss Moyes
"I knew his stuff, I knew his mood, I know everything.
"So, yes, (it was easier) but it is a good experience as well with Van Gaal.
"I think he's a good man, honest, he loves football so he tries do everything for the club."
Source : PA
Source: PA