After a frustrating cameo appearance in the Terriers' 2-0 loss to Swansea City last weekend, Mooy spoke of his excitement about taking on United for the first time at John Smith's Stadium on Saturday (Sunday AEDT).
Huddersfield have had a been a solid start to life in the top flight with two wins, three draws and three losses.
But their first clash against a top-four side in Tottenham two rounds ago exposed their frailties with the West Yorkshire club comprehensively defeated 4-0.
But Mooy remained upbeat saying if his side could eradicate errors and be more ruthless in attack, they could upset Jose Mourinho’s men, who are undefeated in the Premier League so far.
"That's the beauty of football – anything can happen. They are obviously a massive club and it's a big game but we've got to go into it believing in ourselves and trying our best," Mooy told media Friday (Saturday AEDT).
"Hopefully we can get a good result which would be amazing - of course it doesn't happen every week but sometimes you do see the smaller teams beating the bigger ones.
"But to do it we'll have to be at our very best - we have to believe we can get a good result; every player needs to do their jobs and hopefully we can perform well as a team.
"Manchester United are a good team, they'll be right up for it and will want the three points as well. They will be very difficult to play against.
"Little mistakes can prove costly in this division so we have to eradicate them but we also have to be more threatening in the final third as well.
"We've just got to go into every game and try and win it – otherwise what is the point? It's still early doors for us in the Premier League but we're just trying to make the most of it and prove we are good enough to be here."
The 27-year-old also spoke about growing up watching Premier League football and idolising the Socceroos greats like Harry Kewell and Mark Viduka, who played in England.
The former Western Sydney Wanderers and Melbourne City midfielder said he made the move to the UK to face clubs like United and to play against the best players in the world.
"This is why I came to England – to push and test myself and see how far I can go - if I didn't want to do that then I would have just stayed in Australia," he said.
"These are the game you want to play in - when you're younger you always dream big and it's taken a long time to get here but I never gave up and now I have the opportunity to prove myself so I am very proud.
"Manchester United is definitely one of the biggest clubs in the world – you always saw the big names in Australian football like Harry Kewell and Mark Viduka and knew when they were playing on TV.
"I watched every team growing up and didn't just pick one to watch and follow – I just tried to watch as much as I could and the Premier League was the main league that was on all the time in Australia."
