The Ecuadorian was the club's player of the season in 2012, but a number of injuries have seen him struggle to recreate the form that saw him win that award.
However, having still managed to feature on 27 occasions in the Premier League, the winger has admitted that he has been left content with his displays for the Red Devils.
"I suppose it wasn't quite what I was hoping for if you make a comparison with last season," he told . "I've maybe not been able to recreate the form from that year. Maybe not the same level fitness-wise and certainly form-wise.
"But looking back, I'm reasonably happy with my contribution. I've managed to feature in more than 27 games which is special."
The 27-year-old signed for United from Wigan Athletic in 2009.