The 37-year-old, who began his career with Chelsea in 1993, was released by the League Two outfit at the end of last season.
"The last couple of years have been about going up against someone who is trying to send me into retirement," Duberry told the Oxford Mail.
"I've had a few injuries, and my age-to-game ratio is maybe not as high as it could have been because of that, but I have still got a little bit left in the tank.
"My body type is athletic, it's a bit thicker round the waist than it was when I was 21, but I can still get around. I'm not as quick as I used to be, but I think my brain is just as fast, if not faster than it was when I was younger."
Duberry made 13 appearances for Oxford last season.