David O'Leary bought him for £4.5m from Chelsea in 1999 and he made only 20 Premiership appearances under him as manager.
The appointment of Eddie Gray as caretaker has seen the 28-year-old back in the team.
"People say my confidence is high and I look a better player, but I've never had a run of games to compare it to because in the past I've come in for one game and gone out the next," said Duberry.
"I've always said I just need a run of games and people will see the best of me. If I keep my head down and keep playing then you'll see the player O'Leary paid all that money for.
"I've a manager now who believes in me and that's all I've ever wanted. When I was signed, and in being bought for a bit of money, you would think the manager believes in you, but it didn't work out like that.
"But I've stayed confident and Eddie has faith in me and hopefully I'm paying him back for that."