The Portugal international has been at the club since 2007 but has seen his first-team opportunities dwindle, with just seven league starts to his name in last season's title-winning campaign.
Speculation had been rife that he would look elsewhere for first-team football, but the 26-year-old signed fresh terms last Thursday, agreeing a five-year contract at Old Trafford.
He is now ready for the challenge of making himself a regular under manager David Moyes.
"I am very content with my new deal at Manchester United," he told The Daily Mirror.
"This summer was not easy but after a lot of thought and talking to David Moyes, I believe it was the best solution.
"I feel I can offer many things to United. I had other important offers but without a sufficient challenge to make me want to leave United.
"The coach would not guarantee me a place in the XI more than any other player. I know I must work hard to get into this team.
"That is my objective for this season."
He will now hope to impress Moyes if given the opportunity against Crystal Palace on Saturday, having featured in the side's 1-0 loss to Liverpool on September 1.
