The 27-year-old picked up the Player of the Year award at Old Trafford last season but has failed to recreate that form in the current campaign, scoring just once in the Premier League.
The Ecuador international has acknowledged his performances have taken a dip but claims injuries have not helped his cause.
"It's not been quite the season I would have hoped on a personal front," said Valencia, quoted in the Daily Mirror.
"The injuries I've had have held me back a bit. I still get the odd twinge from the last injury I had to my leg and that perhaps affected my progress slightly."
Valencia joined United from Wigan Athletic in the summer of 2009 in a deal reported to be worth in the region of £16million.