Smalling signed a four year deal with United 18 months ago and joined the club last summer.
Following the impressive performances from his debut season, the club obviously believe he is worthy of an improved contract, as well as wanting to ward off any interest from elsewhere.
“This is a great club and, in the short time I have been here, I have already achieved more than I could have ever expected to,” Smalling told the official. “I am looking forward to a long and successful career at Manchester United.”
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