The Irons go into the game off the back of four consecutive wins and with a strong squad while United will be without some key players and have been dogged by inconsistency all season.
Hammers fans inspired by Bilic's East London revolution
West Ham fans are dreaming again thanks to Bilic's East London revolution and the good vibes are clearly inspiring some of the club's supporters.
One such fan, Bobby Guy, has even penned a piece of poetry he hopes will go viral ahead of what is one of the biggest games in a decade for the Hammers.
Bobby said he was inspired by the monologue from Henry V when writing the piece:
Once more into the breach dear friends, once more
We block the M1 with our coaches and roaring motors
In this league there is nothing that so becomes a man than a rousing trip to the northern wastelands
But when the call of the FA Cup resounds in our ears, then be like lions
Flex the muscles, boil the blood, disguise your game face with grim-faced rage
Give your eyes a terrifying look, let them protrude from your skull like brass cannons
Now grit your teeth and flare your nostrils, strain every sinew to its limit
Onwards north you noble Irons sprung from fathers proven on the terraces
From the streets of Plaistow, from the fields of Essex
Prove now that those fathers did indeed beget you
Be examples now to men with less desire and show them how to fight a war
And you, from further reaches of Essex who's limbs were made in England
Show us here what rural men are made of
Let us see that you are worthy to stand shoulder to shoulder with true grit
Which I have no doubt about
I see you descending into Old Trafford, the pit of hell, the so called Theatre of Dreams
Let ours be THEIR nightmare
straining for the start
The game's afoot
Follow your heart
And upon this charge, cry
"God for Slaven, West Ham and Saint Payet!"
Fan hopes poem resonates with fellow Hammers
Bobby has lived in Toronto and New York for the last 20 years but is now back home in Brighton for the club's last ever season at their Boleyn Ground home of 112 years.
And he hopes his fellow West Ham fans will be equally inspired by the poem as nearly 10,000 make the journey to Manchester this weekend.
He said: "The Henry V monologue was the obvious inspiration where he delivered a speech to his weary band of troops to fight the French one more time at Harfleur on the way to Agincourt.
"Of course they won, so the thought of 9,000 strong descending into Manchester made me want to write a similar piece using the same structure."
One thing is for sure, if Bilic's side show the same kind of passion on Sunday they stand every chance of a day out at Wembley in the next round.