Torres was outstanding in victory over Manchester City.
"I'm one that says you have to earn your stripes," Duberry told talkSPORT. "He came with a huge price tag but you have to work hard [to make it].
"His work rate seems to be the thing that is going for him at the minute. Before I thought he didn't really work hard enough, he lost the ball. But now he's chasing down everything, he's being a nuisance.
"I think, as a defender, good centre-forwards have a fear factor. You don't want to play against them. I didn't think defenders were afraid of him anymore but now I think there is a little bit of fear there, which is going to help him."
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