Park, 30, is worried a dip in form could see him moved on by ruthless boss Sir Alex Ferguson despite his tally of four Premier League titles.
He said: “I hope to end my career here now. When I came to United I didn’t expect to be here for this long.
“Looking back I can’t believe I’ve been here six or seven years. Hopefully this club is my last club but you have to prove you deserve it.
“I hope I can improve every single day to deserve that chance.’’