The Belgium international moved from Everton to the Premier League champions on deadline day and is set to make his debut against Crystal Palace on Saturday.
Fellaini is the first central midfielder to sign for United since Owen Hargreaves moved to Old Trafford in 2007, and says he is hopeful he can make a significant impact with David Moyes's side.
|MAROUANE FELLAINI LATEST
|7/5||Marouane Fellaini is 7/5 with BetVictor to score against Crystal Palace
"In the past here you have had Keane, Eric Cantona and David Beckham. I will do my best.
"But there are a lot of good players in the club, so I need to work hard. I want to help the team and I will give everything.
"I will play defensively, but if I can help the team further forward, then I will do that."
Meanwhile, manager David Moyes said the midfielder’s versatility will prove a big asset to the champions and says he will feature in differing role over the course of the season.
"We knew it was an area of the field where we needed to strengthen and we wanted to bring in a central midfielder," he said.
"With Marouane able to play further on as well, he can give us different options. You can’t dismiss his technical ability and his physical presence.
"We have a lot of games coming up, a busy schedule, and I want him to play him different places in different games."