The past three seasons have been a struggle due to a succession of injuries.
He is still to make an appearance this season due to a groin injury that prevented him embarking on United's pre-season tour of the United States.
"Because of my injuries, I have thought about the fact I might have to find something else," he admitted. "Two years ago I thought it would be my last season. Obviously last year I felt the same.
"I recognise this one could be as well.
"I am on a one-year contract. If I don't perform or I feel the club don't want me anymore I will be gone.
"That is life. In the 19 years I have been here, it has happened to better players."