The Ecuadorian joined the Red Devils 10 years ago from Wigan Athletic.
And the full-back has made more than 200 appearances in that time, scoring 25 goals.
But Valencia has only made five this season, struggling with injury, and has not been offered a new contract.
And footage has emerged of the 33-year-old also suffering on the international stage.
In the clip, Valencia is representing Ecuador against the US in an international friendly.
There is nothing to separate the teams as the hour mark draws near.
Valencia forces the 20-year-old into the corner, hoping to clear the ball out.
The United man’s error comes as:
But the forward easily gets the ball under control and turns to face his Ecuadorian opponent.
Pulisic then drags the ball back, keeping the United star waiting for an opportunity to tackle.
But that chance never comes as the American flicks the ball to his left, accelerating away from the defender.
Valencia has no hope as the new Chelsea star sprints away to cross a ball into the box.
The chance is stopped, though, and the 33-year-old is able to clear the ball.
The US went on to win the friendly last Friday 1-0, Gyasi Zardes scoring the winner with nine minutes to go.
This footage was shared on Reddit earlier today.
And the United faithful believed this showed their full-back would not be around for much longer.
“His decline has been rough,” one supporter said.
“Always sad to see it.”
Another commented: “Rubbing salt in the old man’s wounds.”
“He was over performing for a while but age has finally done him in now”
Man Utd fan
While a third believed Valencia should hang his boots up.
“He was over performing for a while,” they said.
“But age has finally done him in now.”
And a fourth added: “His legs are gone now.”
The Red Devils could see a Barcelona defender come into the club, though.