The 31 year-old is in career best form for United.
He told manutd.com: "As a player you’re always trying to improve and learn all the time. That’s what I’ve always tried to do and there comes a stage when, perhaps for a variety of reasons, you hit form and you feel comfortable with the way things are going. It’s probably an experience thing as well. I know what works for me now in different situations and different games, how you cope and how you adapt to that.
"I feel like I’ve improved all the time I’ve been at United. You’re always going to have better spells than others. That's natural and you can’t be on an upward curve all the time or play at your best all the time. But as time has gone on I have improved as a player and I’m still looking to improve even now."