The 23-year-old England international has made 22 appearances in all competitions since August due to a number of fitness problems.
When asked to summarise his campaign, Smalling told the club's official website: "It's one of a bit of frustration because I didn't really get going until November and I had a few little niggling injuries, so I've not been out on the field as much as I would have liked.
"But the team success has been very good and I've been able to contribute something to that, though not as much as I'd have liked. Ultimately it's about the team and the club, and we've been successful so I'm happy with that."
Smalling's last game for United came on April 1 in their FA Cup quarter-final replay defeat to Chelsea.