The Ecuadorian winger has started just three Premier League games this season, following the signing of Ashley Young in the summer.
However, Diego Herrera Larrea, Valencia’s representative, has denied speculation of talks between the two clubs.
"I am aware of rumours of Juventus' interest, but for my part there is nothing concrete," Larrea told calciomercato.com.
"In the past, some Italian clubs were interested in the player but not in recent times.
"I don't think that Juve has spoken with Manchester United because I was not informed, but I cannot exclude it as a possibility.”
Larrea believes a winter move for his client would be unlikely, due to his family commitments, however, he has conceded it is not impossible.
He continued: "I see it as very difficult that he leaves United, first of all because he has recently signed a new four-year deal and because he and his family are very well in Manchester.
"But in football, never say never."